Fishes, Volume 8, Issue 9 (September 2023) – 47 articles

Intestinal bacterial communities play an important role in the growth and health of aquatic animal hosts and have drawn increasing attention. However, the role of the intestinal microbiota in the growth of freshwater prawns remains unclear. Here, the intestinal microbiota of freshwater prawns (Macrobrachium rosenbergii) at different life stages (one, two, and three months old) were investigated using 16S rRNA sequencing. The results showed that community richness and diversity increased with growth, which might be one of the reasons that the prawns maintained a fast growth rate before sexual maturation. Three core phyla were identified in the one-month-old group, namely, Firmicutes (79.24%), Proteobacteria (17.09%) and Actinobacteriota (2.01%). Five core phyla were identified in the two-month-old group, including Firmicutes (47.84%), Proteobacteria (44.22%), Actinobacteriota (1.83%), Acidobacteriota (1.66%) and Bacteroidota (1.24%), and the core phyla in the three-month-old group were similar, except for Acidobacterota, which was not identified. A total of 12 core genera were identified in all samples, and significant differences were observed in the relative abundance of gut microbiota between the three groups (p < 0.05). Exiguobacterium, Lactococcus and Shewanella were the three most significantly differentially abundant genera between stages. In addition, Candidatus Hepatoplasma was detected only in the two- and three-month-old prawn groups. This study provides information on the differences in the intestinal microbiota in different developmental stages, which contribute to adaptation to salinity in the early developmental stage and digestive ability to meet the growth needs of Macrobrachium rosenbergii. Full article

Fishing sector fuel subsidies are designed to increase profitability by reducing costs. However, despite the number of liters of fuel subsidized in 2018 in Mexico, there is no information available on the effectiveness of the subsidies in reducing cost inefficiencies. The purpose of this study was to estimate the cost efficiency of shrimp fishing companies in Mexico, as well as measure the impact of fuel subsidies on the cost inefficiency of the sector from 2003 to 2018. The True Fixed Effects model was used to represent a Cobb–Douglas stochastic production frontier, which included a shrimp fishing inefficiencies model. The results indicate that shrimp fishing companies could reduce their costs by 25% without reducing their catch levels. Fishing companies in the Gulf of Mexico were more efficient than those operating in the Gulf of California and the South Pacific. Fuel subsidies reduce cost inefficiencies, with a greater effect when the subsidy reaches a level of 20% of the total liters of subsidized fuel. Full article

Thermal refuges are becoming increasingly influential for dictating the population status and spatial distribution of cold-water stenotherm salmonids in the mid- to southern extent of their range. The global climate is predicted to continue to warm, and therefore, the overall thermal suitability of freshwater habitats for stream salmonids is predicted to decline in concert. However, stream and river thermal heterogeneity will offer considerable resiliency for these populations. Thermal refuges are formed by many physical processes; common natural refuges include cold tributary plumes, groundwater springs, alcoves, and hyporheic upwellings. However, many anthropogenically formed refuges (such as stratified reservoirs or cold-water tailrace outflows) also exist in hydropower-regulated rivers. The significance of these refuges to stream salmonids depends on their size and temperature differential, but also other habitat characteristics such as their depth, flow velocity, Froude number, and many biotic factors within the refuges. Modern technologies such as drone-mounted thermal infrared cameras and other remote sensing techniques allow for the efficient identification of such refuges, and inexpensive options include the identification of refuges during ice cover using orthophotographs. Behavioural thermoregulation, i.e., salmonids aggregating in cold-water refuges, can be either facultative or obligate and the timing of these events is governed by life stage, species, and population-specific physiologically regulated cumulative thresholds that are inherently related to the recent thermal history, or hysteresis, of each individual. Salmonids appear to have an excellent spatial cognition for locating and relocating cold-water refuges, and their spatial distribution is largely affected by the availability of the cold-water refuges during the warm-water period in many thermally stressed rivers. Gregarious behaviour is the norm for salmonid fishes within the thermal refuges; however, the size/microhabitat hierarchy appears to dictate the within-refuge distribution at the micro-scale. There continues to be a great impetus for protecting—and in carefully determined cases creating—cold-water refuges in the future. A thorough understanding of what a “goldilocks” refuge is for various salmonids and their different life stages will be imperative as cold-water restoration is gaining popularity. Finally, disentangling the roles of the climate-induced and landscape activity-induced warming potential of fluvial freshwater will be important to ensure continued environmentally responsible landscape activities in future waterscapes. Full article

In order to predict the regular temperature change in tuna during the freezing process for cold chain transportation, improve the quality of frozen tuna, and reduce the energy consumption of freezing equipment, a three-dimensional numerical model for freezing tuna of different sizes was established. An unsteady numerical simulation of the air velocity and flow field was combined with an analysis of the freezing process of tuna. This paper also studied the effect of air velocity, temperature, and tuna size on the freezing process. The numerical results show that there was a positive correlation between the cold source environment and the tuna-freezing process. Lower temperatures and higher air increased the velocity at which the tuna moved through the maximum ice crystal formation zone, maintaining a better aquatic product quality. In some cases, however, the smaller tuna models achieved a longer freezing time. Due to the difficulty of obtaining the whole tuna sample, the temperature curve and freezing rate over time obtained during the freezing process were tested using a tuna block of a specific size. The maximum error did not exceed 6.67%, verifying the authenticity and feasibility of the simulation. Full article

Stable isotope ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C) are ubiquitous ecological tracers used to elucidate an organism’s diet and habitat. However, the application of stable isotope ratios to reconstruct a consumer’s ecology relies upon accurate rates for isotopic turnover at both a tissue and species-specific level. This study estimated isotope turnover rates and trophic discrimination factors in four different tissues (liver, digestive tissue, muscle, and skin) with variable metabolic activity in winter flounder Pseudopleuronectes americanus using a controlled diet-switch experiment. Differences in half-lives were noted among the tissues and between the experimental diets for both δ¹⁵N and δ¹³C. The experimental diets of krill and mysis had variability in nutritional composition, resulting in similar turnovers in δ¹⁵N but slower turnovers in δ¹³C for fish fed krill. Turnovers in both δ¹⁵N and δ¹³C were strongly influenced by metabolism, with the contribution reaching up to 98%, as fish exhibited minimal overall growth. The results of this study demonstrate the importance of considering differences in the catabolic activity of tissue maintenance for fish exhibiting minimal growth, as well as differences in metabolic assimilation of dietary sources that vary in their protein and lipid contents. Full article

This report aims to characterize and reuse fish head powder (FHP) as a potential carbon/nitrogen source for microbial fermentation to produce prodigiosin (PG), and to evaluate its novel anti-fungal effect via an experimental and docking study. FHP has high protein (30.25%) and lipid (5.12%) content and a diversity of elements, which suggests that FHP is a potential substrate for microbial fermentation. Serratia marcescens TNU01 was screened as the most effective strain to produce PG from FHP. Further experiments indicated that the combination of FHP and crude chitin at the ratio of 9/1 and used at 1.5% as a C/N source for fermentation significantly enhanced PG production. Supplementing a minor amount of 0.05% Ca₃(PO₄)₂, 0.03% K₂SO₄ also positively affects PG yield production. The fermentation using a bioreactor system (type of 14 L) achieved the highest PG yield production (6.4 mg/mL) in a short cultivation time (10 h) in comparison with the highest PG yield (5.8 mg/mL) obtained after 36 h of fermentation in a flask. In the anti-fungal evaluation of various plant pathogen fungal strains, PG demonstrated efficacy against Fusarium solani F04. The molecular docking results also showed that PG effectively interacted with targeting protein 3QPC of F. solani with good binding energy (DS—9.2 kcal/mol) and an acceptable RMSD value (0.94 Å). In this study, we provide a novel application of FHP for the eco-friendly production of PG, which can potentially used for the management of Fusarium solani. Full article

Levels of dietary carbohydrates and lipids have important effects on the growth, health, and glycolipid metabolizing capacity of the hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). This experiment evaluated the effect of carbohydrate to lipid ratios (CHO:L ratio) on growth, serum biochemical indices, intestinal morphology and activity of digestive enzymes, and the ability to metabolize carbohydrates and lipids in the hybrid grouper. Six iso-nitrogenous (500 g/kg) and iso-energetic (190 MJ/kg) feeds with CHO:L ratios of 0.82, 1.03, 1.28, 1.58, 1.94, and 2.27 were formulated. The 720 groupers with an initial body weight of 7.76 ± 0.08 g were sorted into 24 fiberglass buckets of 30 fish each. Feed was delivered twice daily at 8:00 and 16:00 to apparent satiety for 56 days. The results showed that the growth performance of the groupers was not significantly affected by the diet. Based on the specific growth rate (SGR), the optimal CHO:L ratio was 1.72 for the groupers by the second-order polynomial regression model. The intestinal trypsin and lipase, and the hepatic trypsin activities of the groupers showed a maximum in the 1.58 group. The intestinal muscle thickness in the 1.94 group and the villus length in the 1.58 group were significantly greater than in the 0.82, 1.03, 1.28, and 2.27 groups. The glycogen synthase, pyruvate kinase, and hexokinase activities of the liver were significantly higher in the 1.58 group than in the 0.82 and 2.27 groups. The hormone-sensitive triglyceride lipase, adipose triglyceride lipase, acetyl-CoA carboxylase, and carnitine palmitoyl transferase of the liver showed significantly higher activities in the 1.58 group than those in the 0.82 and 1.03 groups. These results showed that based on the SGR of the groupers, the best CHO:L ratio was 1.72. An appropriate dietary CHO:L ratio can reduce the lipid deposition of the fish body, liver, and muscle, as well as improve the intestinal morphology and activities of liver carbohydrate and lipid metabolism enzymes. Full article

The present study was conducted to investigate the effects of dietary fermented cottonseed meal (FCSM) substitution for fish meal on intestinal enzymatic activity, inflammatory and physical-barrier-related gene expression, and intestinal microflora of juvenile golden pompano. The 375 golden pompanos were divided into 15 groups of 25 fish each, with three replicates for each experimental group. The fish were fed five experimental diets (0 (FM), 12.5% (CSM12.5), 25% (CSM25), 50% (CSM50), and 100% (CSM100) substitution levels) for 8 weeks. The fish were reared and fed the experimental diets under a natural-day light cycle. Compared with the control group, the activities of AMY (amylase) enzymes in the CSM12.5 group and all other groups were elevated (p < 0.05). The CSM25 group exhibited a considerable up-regulation of IL-10 (Interleukin-10) expression relative to the FM group (p < 0.05). With an increase in dietary FM substitution with FCSM from 0 to 25%, the relative expressions of NF-κB (Nuclear factor kappa-B), IL-1β (Interleukin-1 beta), and IL-8 (Interleukin-8) were down-regulated. In this study, the relative expressions of ZO-1 (zonula occluden-1) and Occludin were up-regulated, and those of Claudin-3 and Claudin-15 significantly up-regulated, when the FCSM substitution ratio was 25%. The results of high-throughput sequencing of the intestinal microflora showed that ACE indices the lowest in the CSM25 group, which was significantly different from those in the CSM100 group (p < 0.05). The CSM50 group had the highest Shannon and Simpson indices and the highest community diversity. In addition, replacing a high percentage of fish meal with FCSM can negatively affect the intestinal flora of fish. In this study, the 25% substitution ratio improved nutrient absorption, reduced intestinal inflammation, improved intestinal physical barrier damage, did not affect intestinal microecology, and had no adverse effects on fish. However, substitution of a high proportion of FM with FCSM negatively affects the intestinal microflora and nutrient absorption capacity of fish. Full article

Biofloc technology (BFT) as an efficient aquaculture alternative is attracting attention for boosting biosecurity with minimal water exchange and reduced feed intake. BFT relies on applying organic carbon to maintain a high C/N ratio above 10, which allows heterotrophs to assimilate toxic nitrogen. A high percentage of carbon loss is thus generated from BFT. For this review, a thorough search of the relevant literature was conducted to gather valuable information on the optimization of carbon utilization. The keywords searched included ‘BFT’, ‘carbon use efficiency’, ‘carbon conversion’, ‘carbon retention’, ‘carbon emission’, ‘carbon loss’, and ‘carbon release’. The current review discusses the possible effects of various C/N ratios, carbon types, addition strategies, and technology integration with respect to the optimized carbon utilization in BFT. Given the extreme lack of accessible research, it was concluded that the carbon utilization in BFT is still in its initial research stage. Anyhow, this review sheds light on plausible approaches for boosted carbon utilization by adopting slow-release carbon, reducing carbon input, integrating with other technologies, and enhancing interactions between functional microbes within BFT, thereby contributing to sustainable aquaculture. Full article

A multi-mesh trammel net has been developed and used for sampling freshwater fishes. However, little is known about the catch efficiency of the net. This research investigated the catch efficiency of a multi-mesh trammel net (nominal mesh size; 10.0, 30.0, 50.0, and 70.0 mm) for fish sampling in the Yangtze River of China. Catch composition and factors affecting catch per unit effort based on fish number (CPUE_N), weight (CPUE_W), and species number (CPUE_S) were analyzed. The results showed that the net was capable of capturing a wide range of fish sizes (total length, 5.5 to 121.0 cm) and species (n = 50). Increasing soak time from 9.4 to 24.0 h resulted in a decrease in CPUE_N and CPUE_W while a longer soak time increased CPUE_S. CPUE_N, CPUE_W, and CPUE_S varied significantly with fishing locations. The net provides a potential complement to the current fish sampling techniques used in freshwater ecosystems (e.g., large rivers, lakes, and reservoirs). The findings of this research help to improve our understanding of the catch efficiency of the multi-mesh trammel net and provides insight into better designs for gears and methods for sampling diverse fish sizes and species. Full article

Over the last two decades, the growth of the fisheries sector in Indonesia has shown an increasing trend; however, behind the rapid development of this sector, the role of small-scale fisheries as one of the main actors supporting the whole industry is often neglected. They remain poor and continue to conduct fishing activities traditionally. Therefore, this study aims to describe the real situation of small-scale fishers, analyzing the fishers’ ownership of the boat they use, analyzing their income level to reveal their poverty status, and analyzing the factors affecting their income. The regression analysis results indicate that boat category, sea fish catch, fish selling price, fixed costs, and variable costs have significant effects on fishers’ net incomes. Full article

River ecosystems are exposed to a multitude of stressors, including increasing pesticide run-off driven by precipitation and irrigation. Pyrethroids are the fourth major group of insecticides in use worldwide and have extremely negative effects on aquatic fauna. In this study, we aimed to assess the effects of an acute 2 h sub-lethal exposure to different levels of the pyrethroid esfenvalerate on the swimming behaviour of two Cypriniformes species: the native Iberian barbel (Luciobarbus bocagei) and the non-native invasive bleak (Alburnus alburnus). The experimental set-up consisted of previous exposure to three esfenvalerate concentrations (control, 1.2 (low), and 2.0 (high) μg/L) before being stocked in a three-artificial-flume-channel mesocosm for behavioural trials through direct observation. Monitored behaviours included (i) routine activity, (ii) shoal cohesion, and iii) boldness. Significant differences in fish behaviour were detected for the native species (barbel), as individuals spent significantly more time holding position (i.e., resting) in the control (44.9%) than in the high esfenvalerate concentration (25.2%). Concordantly, control barbels were also found to perform more directional changes than the ones exposed to high esfenvalerate concentrations. Behavioural changes were also found for boldness, measured by the proportion of fish attempts to negotiate the upstream ramp, which were significantly higher in the control (37.4%) and in the high concentration (41.5%) compared to the low one (21.1%). Finally, regarding shoal cohesion of the barbel, it was tighter in the control (81.3%) than in the low- (70.5%) and high- (71.1%) esfenvalerate treatments. For the invasive bleak, there were no significant differences in any of the behavioural traits upon previous exposure to an increasing esfenvalerate concentration. This experimental study demonstrated that even short-term exposure to the pyrethroid esfenvalerate was sufficient to alter the behaviour of a native Cypriniformes fish species while not affecting the non-native species. This may confer greater competitive advantages to non-native fish species in the context of global changes. Full article

As recreational fishers act relatively autonomously, management relies heavily on voluntary compliance. Therefore, understanding fishers’ views on management options can be beneficial. This study used a two-phase approach of face-to-face interviews and subsequent online questionnaires to evaluate recreational fishers’ salient views on issues affecting the Blue Swimmer Crab (Portunus armatus) and Black Bream (Acanthopagrus butcheri) fisheries in Western Australia as well as current and potential management arrangements, including stock enhancement. The strength and heterogeneity of views were also determined. Minimum size limits were mainly considered acceptable or very acceptable, with restricting recreational fishing and spatial closures the least supported management options for both species, in addition to maximum size limits for crabs. These views were not always consistent across fishing locations for each species and among types of crab fishers, indicating heterogeneity in views. Stocking was the most acceptable of the management measures not already utilised for crabs and among the most popular for bream fisheries. Recreational fishers of both species believed stock enhancement could have strong positive outcomes for the abundance of their target species and increase their subsequent catches. They also recognized that some negative outcomes, e.g., increased fishing pressure and environmental issues, might occur but considered them unlikely. Full article

Aminotransferases are enzymes found in living organisms that catalyze transfer reactions between amino acids and keto acids, crucial for amino acid metabolism and synthesis. Aminotransferase classes I and II play a vital role in regulating osmolarity, protecting cells, and improving metabolic homeostasis and cellular fitness. To investigate the characteristics of the aminotransferase class I and II gene family and their roles in osmotic pressure regulation in the Jinjiang oyster (Crassostrea ariakensis), the gene structure, chromosomal localization, and phylogeny were characterized and the genes’ expression in the gill under high-salt stress was analyzed. In this study, eighteen Aminotransferase class I and II genes, including SPTLCa and SPTLCb, SPTa and SPTb, ALAT2a and ALAT2b, KAT3a and KAT3b, and ASTa, ASTb and ASTc, were identified. The physicochemical properties of 11 family members were stable, with their instability factors less than 40. Subcellular localization prediction showed that aminotransferase classes I and II were localized in the cytoplasm or mitochondria. Chromosomal localization results showed that the 18 aminotransferase class I and II genes were located on eight chromosomes. All members of this gene family had the Aminotran_1_2 structural domain which is associated with osmotic pressure regulation by adjusting the conversion reaction between amino acids and keto acids. Most gene expressions showed an initial increase followed by a decrease from 0 h to 12 h when the oysters were challenged by acute stress using artificial seawater with a salinity of 40. However, the expression of CarAGT2 and CarKAT3b genes showed an increased trend with increasing stress time. This study systematically investigated the bioinformatics characteristics of the aminotransferase class I and II gene family in C. ariakensis and their role in osmotic pressure regulation, which provides scientific data for understanding the potential functions of these genes in physiological adaptation, thereby expanding the research on osmoregulation in bivalves. Full article

The size of chum salmon juveniles is crucial to their survival. In order to understand the population status and migration patterns of juvenile chum salmon in the waters of the Amur River in China, this study investigated the status of juvenile chum salmon resources and their basic biological characteristics in the Amur River and the Ussuri River in China. The results showed that the average catch per unit effort (CPUE) of chum salmon in river margins was 0.140 ind·10⁻³ m³ for the Amur River and 0.255 ind·10⁻³ m³ for the Ussuri River. Chum salmon migrate downstream, mainly in mid-May in the Amur River and in early May in the Ussuri River, and no fish was caught in the rivers after June. Most chum salmon migrated when the water was between 10 and 14 °C. The average FL (fork length) and BW (body weight) of the Amur River samples were 37.1 ± 2.9 mm and 0.42 ± 0.09 g, respectively, while the Ussuri River samples’ FL and BW were 34.9 ± 3.7 mm and 0.36 ± 0.08 g, respectively. The empty stomach rate of the samples was zero, and the prey category of the samples was composed of fish, aquatic insects, copepods, and cladocerans, of which Ephemeroptera had the largest percentage index of relative importance (IRI%), with a value of 58.45%. The size of the downstream-migrating juvenile chum salmon in this study is similar to the size of those in some other rivers, and the CPUE varies depending on the river conditions. Full article

To investigate the age composition, growth pattern, mortality, and exploitation rate of Triplophysa scleroptera in the upper reaches of the Yellow River, we measured the total length (L) and body weight (W) of 347 individuals based on three sampling surveys from 2022 to 2023. The otoliths were used in this investigation to determine age. The total length of the collected samples ranged from 5.69 cm to 18.40 cm, body weight ranged from 1.65 g to 50.22 g, and the age ranged from 1 to 7 years old. The relationship of total length and body weight was $W=0.009L^{2.942}$ for the total samples, and the growth pattern observed in the study belongs to the isometric type. The von Bertalanffy growth equation revealed that the fish had an asymptotic total length L_∞ of 37.536 cm, and the growth coefficient K was 0.064 yr⁻¹. Total instantaneous mortality rate (Z) of total samples calculated by the age-based catch curve method was 1.092 yr⁻¹. The average instantaneous rate of the natural mortality (M), estimated by three different methods, for the total samples was 0.237 yr⁻¹. The instantaneous rate of fishing mortality (F) for the total samples was calculated as 0.855 yr⁻¹, and the exploitation rate (E) was determined as 0.783. As a whole, compared with other Triplophysa fishes, the growth rate of T. scleroptera in the upper reaches of the Yellow River is relatively slow, and the population of T. scleroptera has been overexploited. It is crucial to establish some effective management strategies to protect this species. Full article

In the cultivation of Mytilus unguiculatus, the broodstock are shade-dried to stimulate sperm and egg production. To identify the functional genes affecting gonad development in M. unguiculatus, the transcriptome of gonads in mussels stimulated by shade-drying and those not stimulated were compared. Differential gene expression analysis revealed that there were 22 differentially expressed genes (DEGs) in the testis and 70 DEGs in the ovary among the experimental groups. KEGG enrichment analysis identified a total of 11 pathways that might be related to environmental stimuli affecting gonadal development. Nicotinic acetylcholine receptors (AChRs), the cholecystokinin A receptor (CCKAR), hypocretin (orexin) receptor 2 (HCRTR2), and gamma-aminobutyric acid type B receptor (GABBR) were highly expressed in the neuroactive ligand-receptor interaction pathway, indicating that these genes might be involved in the transduction of environmental information that stimulates gonadal development. Meanwhile, nuclear receptor co-repressor 2 (NCoR2) was highly expressed in the notch signaling pathway, indicating that NCoR2 might be involved in the regulation of gonad development. To validate the transcriptome data, we selected five DEGs in the KEGG signaling pathway, including AChRs, CCKAR, HCRTR2, GABAB, and NCoR2, for real-time quantitative PCR (RT-qPCR), which produced results consistent with the RNA-Seq data. The transcriptome analysis and gene pathway identification in this study have enhanced our comprehension of the reproductive mechanisms in M. unguiculatus. Full article

Salmon lice are one of the biggest challenges to sustainable salmonid aquaculture. The species display high evolutionary potential, which is evident by its development of resistance to numerous chemical compounds used for delousing. In response to this, salmon farms now use non-chemical delousing methods to minimize the damage done by salmon lice, including heavy reliance on cleaner fish. Anecdotal reports from farmers and fish health personnel in areas where cleaner fish are used have suggested that salmon lice are becoming less pigmented, potentially making them harder for cleaner fish to visually detect. This experiment investigated changes in the pigmentation of salmon lice in relation to the use of cleaner fish, louse stage and sex, temperature, preferred salmon swimming depth, daylength, and salinity. Salmon lice were sampled from snorkel cages on a commercial salmon farm where three cages were stocked with farmed lumpfish and ballan wrasse, and three cages were without cleaner fish. Water temperature, salinity, and depth were recorded using a conductivity, temperature, and depth recorder. Pigmentation was measured via photographic analysis of individual lice. Although louse pigmentation varied considerably throughout the experiment, using cleaner fish throughout a single production cycle did not reduce average louse pigmentation compared to control cages. On average, male lice were significantly darker pigmented than females, but otherwise there were no patterns in louse pigmentation in relation to life stage, salinity, temperature, or daylength. Salmon lice exhibit a high degree of evolvability and have become resistant to every chemical removal treatment developed thus far. The present data suggest that, with the densities and species of cleaner fish commonly used in commercial salmon production, there is not strong directional selection on louse pigmentation. Lice, at least with regard to visual appearance, are not likely to adapt in a way which reduces cleaner fish efficacy anytime soon. Full article

Intensive culturing of hybrid yellow catfish (Pseudobagrus vachellii ♂ × Tachysurus fulvidraco ♀) has increased their mortality. Astragalus membranaceus has been used as an immune stimulant and antioxidant in fish for several years. A. membranaceus was decocted and mixed with the diet. After feeding for 28 d, the hybrid yellow catfish were challenged with Aeromonas hydrophila. To better understand the function of A. membranaceus in the defense of hybrid yellow catfish against A. hydrophila, we analyzed the spleen transcriptome data and relative percentage survival (RPS). There were 396 differentially expressed genes (DEGs) between the A. membranaceus and control groups at 24 h after A. hydrophila stimulation, including 263 upregulated and 133 downregulated DEGs. A significant enrichment of DEGs was found in the A. membranaceus group when the GO enrichment terms in the spleen were analyzed. The qRTPCRresults for the five upregulated and two downregulated DEGs from the spleen, intestine, and liver were consistent with the transcriptome data. The relative percentage survival of A. membranaceus was 85.71% after the fish were challenged with A. hydrophila. Full article

While few have contemplated the potential impacts of climate change on small-scale fisheries and fishermen in the Colombian Pacific, understanding these effects is crucial for devising effective adaptation strategies. This study presents the outcomes of a vulnerability assessment related to climate change for fishermen in the Colombian South Pacific. The assessment employed a multivariable model that considered the sensitivity of marine and coastal ecosystems that support fishing resources alongside fishermen’s adaptability to changes in the biophysical environment. Socioeconomic factors were also scrutinized. The study revealed that 80% of the surveyed fishermen are at a medium to high level of vulnerability due to changes in the distribution of key commercial species, which influences the productivity of their traditional fishing sites. Their vulnerability is primarily attributed to low usage of fishing technologies, the boat engine’s limited propulsion capacity, and a lack of diversity and sustainability in fishing gear. These elements increase their reliance on fishing sites close to the coast (approximately 3 km to 5 km from the shoreline), resulting in a low adaptive capacity for the fishermen. The dominant factor driving the sensitivity component was the economic significance of the fishing gear and the fact that the gear could be more diverse and durable. These findings provide a critical scientific basis for assessing the fishing sector’s vulnerability to climate change and informing future collaborative decision-making in managing small-scale fisheries in the Colombian South Pacific Ocean. Full article

This study investigated disease outbreaks in farmed Oreochromis niloticus (Nile tilapia) in Siavonga among small-scale cage culture farms on Lake Kariba in order to establish bacterial etiological agents associated with fish mortality and to determine their antibiotic susceptibility. A total of 300 fish samples from 11 farms were aseptically collected and bacteria were isolated from the kidney, liver, brain, and spleen. The isolates were identified using their morphological characteristics and conventional biochemical tests. The antibiotic susceptibility of selected bacteria was determined by the Kirby–Bauer disc diffusion method. The following well-known fish pathogens were identified at a prevalence of Aeromonas spp. (13%), Pseudomonas spp. (10.3%), Micrococcus spp. (9.7%), Klebsiella spp. (8.7%), Lactococcus spp. (7.3%), Streptococcus spp. (7.0%), and Acinetobacter spp. (7.0%). All the isolates tested were susceptible to doxycycline, and complete resistance to ciprofloxacin, co-trimoxazole, and cephalothin was recorded in the Bacillus spp. The observed resistance could be attributed to bacteria from terrestrial sources as fish farmers do not administer antibiotics to fish. To our knowledge, this is the first study to establish the occurrence of several bacterial species infecting tilapia in Zambia and the first to determine the antibiotic susceptibility of fish bacteria among small-scale farms on Lake Kariba. The current study provides baseline information for future reference and fish disease management on Lake Kariba and in Zambia. Full article

Aquaculture of marine ornamental fish could potentially reduce the fishing pressure on wild stocks by the global aquarium trade, but its expansion is often constrained by the limited understanding on the biology and early life history of candidate species. The orchid dottyback Pseudochromis fridmani is a valuable and popular marine ornamental fish, but scientific reports on its baseline biology, especially the egg filial cannibalistic behaviour, are scarce. The present study documented key aspects of reproductive biology and early ontogeny of P. fridmani in captivity, including reproductive behaviour, patterns of spawning and filial cannibalism throughout a 12-month period by seven pairs of brood fish, as well as the embryonic and larval development. The results showed that the captive spawning of the broodstock pairs generally occurred every 5–11 days, most commonly every 6–8 days, throughout a year. Despite feeding the brood fish to satiation throughout the data collection period, the average monthly rate of egg filial cannibalism reached 55 ± 37%, but the cannibalism frequency appeared to be pair-specific. The egg incubation duration was approximately 96 h at 27 ± 1 °C, and the development of embryos from cleavage, blastula, gastrula, and segmentation to the pharyngula stage is herein described in detail. The newly hatched P. fridmani larvae possessed important structures and organs for first feeding, including pigmented eyes, developed jaws, and a straight-tube gut. The 0 to 14 days post-hatching (DPH) period appeared to be an important larval stage, as P. fridmani larvae were observed to complete major changes in morphology, gut development, and phototactic behaviour by 14 DPH. Under the culture conditions of this study, the earliest transition to the juvenile stage was observed on 31 DPH, and the majority of fish became juveniles by 56 DPH. The results of this study inform baseline aquaculture production protocols and direct future research, particularly to reduce filial cannibalism through broodstock management and to improve larval culture through supporting the early ontogenetic development of P. fridmani. Additionally, these findings form a foundation for further studying the biology and ecology of P. fridmani in the wild. Full article

The introduction of non-native freshwater fish is a primary cause of aquatic biodiversity loss at global scale. Such introductions have a severe impact on freshwater ecosystems in terms of competition, predation, habitat alteration, genetic pollution and transmission of diseases and parasites. A systematic review was conducted on the helminths parasites of freshwater fish in the context of species introduction and a total of 199 publications were retrieved between 1969 and November 2022. Several scenarios may arise when a new fish species arrive in a recipient area. Non-native fish hosts can co-introduce their parasites without transmitting them to native fish (e.g., the case of North American Centrarchidae and their Monogenea parasites). Another possible outcome is the transfer of these parasites to the native fish fauna (spillover, e.g., the cases of the Nematoda Anguillicola crassus Kuwahara, Niimi & Itagaki, 1974 and the Monogenea Gyrodactylus salaris Malmberg, 1957). Reciprocally, non-native fish hosts may acquire parasites in their new distribution range whether these parasites are native or were previously introduced (e.g., the cases of Ponto-Caspian Gobiidae and the Chinese sleeper Perccottus glenii Dybowski, 1877). Acquired parasites can then be spilled back to the native fauna. This phenomenon is of particular interest when non-native fish hosts influence the dynamics of zoonotic parasites. Full article

The type of protein source in diets has many effects on shrimp. In this study, Litopenaeus vannamei with an initial body weight of 3.68 ± 0.002 g were fed for 8 weeks on three experimental diets (isoproteic: 41.00%; isolipidic: 7.61%) that were formulated using fish meal (FM), Chlorella sorokiniana (CHL), and Clostridium autoethanogenum protein (CAP) as the primary protein sources, respectively. This study examined the growth, non-specific immunity, intestinal digestion, and microbiota of L. vannamei after the feeding experiment concluded. Compared to the FM group, the findings indicate that the weight gain rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) of L. vannamei were notably enhanced via dietary CAP. The CHL group exhibited the highest levels of catalase (CAT), phenoloxidase (PO), and superoxide dismutase (SOD) activities in the gills of L. vannamei, whereas the FM group had the lowest levels. Conversely, the malondialdehyde (MDA) content showed the opposite trend. Both dietary CHL and CAP promoted the digestive enzyme activities of L. vannamei, with dietary CAP having a more pronounced promotional effect. An analysis of alpha diversity indicated that the consumption of dietary CHL substantially enhanced the abundance and diversity of microbiota in the intestinal tract of L. vannamei. Furthermore, the dietary CHL significantly increased the colonization of immune-associated beneficial bacteria and inhibited the colonization of pathogenic bacteria in the intestinal tract of L. vannamei, whereas dietary CAP mainly increased the colonization of growth-associated beneficial bacteria. Functional predictions showed that different dietary protein sources affect various metabolic activities and signaling pathways of L. vannamei, and some functions, including signal transduction, cell motility, and the immune system, were significantly enhanced in the CHL group. In summary, both dietary CHL and dietary CAP promoted growth and immunity in L. vannamei compared to dietary FM. The results of this study could be helpful for the sustainable development of shrimp farming. Full article

This experiment aims to investigate the effects of partial replacement of fish meal (FM) by soybean meal (SBM) and/or fermented soybean meal (FSBM) on the growth, serum biochemistry, digestion, antioxidation, immunity, and mTOR signaling pathway of juvenile coho salmon (Oncorhynchus kisutch). Four iso-nitrogen and iso-lipid diets were designed and fed to four groups of juvenile coho salmon (152.25 ± 2.96 g) in triplicate for 10 weeks. The four diets were the G0 diet (control group, containing 28% FM protein), the G1 diet (containing 10% SBM protein and 18% FM protein), the G2 diet (containing 5% SBM protein, 5% FSBM protein, and 18% FM protein), and the G3 diet (containing 10% FSBM protein and 18% FM protein). It was found that compared with the G0 diet (control group), the activities of catalase (CAT), superoxide dismutase (SOD), pepsin, trypsin, α-amylase, and lipase, and the expression levels of mammalian target of rapamycin (mtor), protein kinase B (akt), phosphatidylinositol 3-kinase (pi3k), plant ribosome S6K protein kinase (s6ks), and lysozyme (lyz) genes, of juvenile coho salmon fed the G3 diet increased significantly (p < 0.05), and the expression levels of tumor necrosis factor (tnf-α), interleukin-1β (il-1β), and interleukin-6 (il-6) genes of juvenile coho salmon fed the G3 diet decreased significantly (p < 0.05). However, there were no significant differences in growth, muscle composition, and serum biochemistry of juvenile coho salmon fed the G3 diet compared with the G0 diet (p > 0.05). In conclusion, replacing 10% FM protein with FSBM protein could improve the digestion, antioxidation, immunity, and mTOR signaling pathway of juvenile coho salmon. Full article

The effect of thermophilic species invasion in the eastern Mediterranean is well-noted in the literature. During the last decade in western Greek waters, small-scale fisheries (SSF) catches exhibit increased relative contribution of rabbitfishes, which have originated from the Red Sea and inhabited the country’s southeastern part since the Second World War. This study has used quantitative and qualitative information to assess the short-term economic effect of the rabbitfishes’ expansion in the SSF métier targeting the indigenous thermophilic parrotfish in the South Ionian Sea. The short-term micro-level negative economic effects of the rabbitfishes’ invasion and the corresponding adverse effects on fishers’ economic wealth have been estimated. The results indicate attitudinal differences among fishers, although their local ecological knowledge may enable them to avoid rabbitfishes’ hot spots and mitigate the respective economic losses, that particularly for smaller SSF vessels already seem to be quite important. As climate warming may further facilitate the expansion of rabbitfishes, outcompeting parrotfish, the latter métier may eventually become economically unsustainable. Fine-scale analysis at the métier level enables addressing the specificities of social-ecological systems and can contribute to informed and more effective decision making related to SSF, which is an important building block of Mediterranean coastal communities. Full article

Carbon stable isotopes (δ¹³C) are widely used in ecological studies to understand diet, food web dynamics, and movements of marine fishes. Still, δ¹³C is influenced by lipid content and often requires chemical extraction or mathematical correction. Here, we developed a species-specific mathematical lipid correction for white muscle tissue of yellowfin tuna (Thunnus albacares), a highly migratory finfish of considerable economic and ecological value. Lipid extraction was conducted on yellowfin tuna white muscle tissue (C:N range: 2.96–6.49), and both linear and non-linear lipid correction models for δ¹³C were fitted and assessed. Lipid extraction increased δ¹³C, and to a lesser extent, δ¹⁵N values in yellowfin tuna white muscle tissue, but had no effect on δ³⁴S. Both non-linear models provided better fits to the data than the linear model, suggesting an asymptotic relationship between C:N and ∆δ¹³C. Results support the growing body of evidence that C:N ratios can be used to predict lipid corrected δ¹³C and highlight the value of mathematical correction approaches. We provide species-specific parameter estimates that can be used for lipid correction of white muscle tissue for δ¹³C analysis in yellowfin tuna and similar species for which species-specific models have yet to be developed. Full article

The study aimed to evaluate the effect of inorganic mercury (iHg) on the sperm quality, embryos, and larvae of Prochilodus magdalenae. Two experiments were carried out. In experiment 1, semen was activated with contaminated water at different iHg concentrations (0.0, 25, 50, 100 µg/L) and sperm kinetics were analyzed with a computer-assisted semen analysis (CASA) system. In the second trial, 2 g of oocytes were fertilized with 50 µL of milt, activated with contaminated water at different iHg concentrations (0.0, 25, 50, 100 µg/L), and maintained that way during the first hour of incubation. Samples were taken every 3–4 h until hatching to identify embryo deformations. Fertilization and hatching rates were estimated. The survival of newly hatched larvae (1 day) and larvae eight days post-hatching (dph) was also assessed. The results show that the quality parameters of semen treated with contaminated water at different iHg concentrations (25, 50, 100 µg/L) were altered and showed significant differences (p < 0.05) from the control group (0 µg/L). Total motility decreased (9.8–13.2%) and the amount of immotile sperm increased (3-fold) relative to values in the control group. A significant increase in oocyte diameter and a decrease in fertilization and hatching rates were observed with the higher iHg concentrations (50–100 µg/L). Embryo deformations (>40%) such as scoliosis, lordosis, and microcephaly were observed, as well as premature hatchings. The larval survival at 1 dph was reduced between 25% (25 µg/L) and 97.2% (100 µg/L) relative to that in the control group. The results suggest that bocachico semen, embryos, and larvae are sensitive to contamination with iHg from 25 µg/L. Full article

The aquaculture production of pikeperch has reached commercial scale in a number of European countries, but the high mortality of early life cycle stages and minor understanding of nutritional requirements are still major bottlenecks. To investigate the fate of fatty acids during early development, weaning and rearing, pikeperch larvae and juveniles from a commercial recirculating aquaculture system (RAS) were sampled over 2 months for morphometric data, as well as fatty acid composition, with a total of 6 sampling days, with four to five replicates per sampling day and between 1 and 25 pikeperch larvae per individual sample, depending on larval biomass. The biomass of sampled pikeperch larvae varied from 0.1 to 420 mg (dry mass DM), depending on the age of the larvae, and the initial length of the pikeperch larvae was about 4.5 mm. Our data confirm that, accompanied by an exponential increase in dry mass, total fatty acids (TFAs) in larval tissues increased with the beginning of exogenous feed uptake and were depleted between days 13 and 25 post hatch, most likely associated with the weaning and metamorphosis of the larvae. We conclude that all fatty acid classes may serve as metabolic fuel during metamorphosis, but the ultimate fatty acid composition is strongly impacted by the available feed. The chosen diet probably caused a lack of alpha-linolenic (18:3n-3; ALA) and docosahexaenoic acid (22:6n-3; DHA) during larval development and a shortage of vaccenic (18:1n-7), alpha-linolenic (18:3n-3; ALA) and arachidonic acid (20:4n-6; ARA) in juvenile pikeperch. This led to low DHA/EPA ratios 13 days post hatch, a high EPA/ARA ratio at days 41 and 56 post hatch and a fluctuating ratio of alpha-linolenic acid to linoleic acid (18:2n-6; LA). A temporary lack of essential fatty acids can cause dysfunctions and eventually mortalities in pikeperch larvae and juveniles. Despite high larval growth rates, the biochemical composition of the first fed Artemia and microdiets was most likely not sufficient and in need of improvement. We suggest that deficiencies must be compensated, e.g., through the substitution of the offered Artemia with more suitable live feed organisms, such as freshwater rotifers, and the enrichment of current microdiets in order to prevent high mortalities during pikeperch rearing and weaning. Full article