Aquac. J., Volume 3, Issue 2 (June 2023) – 6 articles

Symsagittifera roscoffensis is an intertidal Acoel flatworm that forms a symbiotic relationship with the alga Tetraselmis convolutae. Members of the genus Tetraselmis are known to have a high nutritional value and have been widely used to enrich intermediate prey for fish within the aquaculture industry; therefore, S. roscoffensis could be a good candidate as a trophic shortcut to deliver algal nutrition to fish. In this study, we investigated the likelihood of five ornamental tropical freshwater and six ornamental marine fishes to consume this worm, either as live feed or in freeze-dried form. We also tested the ability of S. roscoffensis to form a symbiotic relationship with alternative algal species, analysing the nutritional profile of S. roscoffensis when grown in different media. All the experimental fish consumed live worms to some degree, with the exception of one species (Meiacanthus grammistes); the response time to the worms ranged from 1.1–68.6 s for freshwater ornamental species to 1–24 s for marine ornamental species, and in most cases, this was comparable to or shorter than their response time to the reference diet Artemia. The fishes showed no negative effects after consuming the worms. We obtained similar results with freeze-dried worms in terms of the number of worms eaten, response time, and feeding time. Symsagittifera roscoffensis was able to form a symbiotic relationship with all the tested algal species of the genus Tetraselmis, but not with members of other genera. Worms grown in nutrient media (f/2 and f/4) had significantly higher contents of protein, pigments, and total and polyunsaturated fatty acids, including eicosapentaenoic acid (20:5n − 3) and α-linolenic acid (18:3n − 3), than those grown in seawater. These results show that S. roscoffensis was acceptable to many ornamental fish species, delivering key algal ingredients that are beneficial to fish health; hence, it is a promising alternative to conventional fish feeds for the ornamental pet trade. Full article

The giant freshwater prawn (GFP), Macrobrachium rosenbergii, is one of the largest palaemonids in the world, found in tropical marine, estuarine, and freshwaters, and is among the most commercially cultured crustaceans. According to research, mature males usually develop differences in cheliped morphology, growth characteristics, and agonistic behavior. The identification of such morphotypes is critical for effectively managing and handling prawns. The present study aimed to describe the GFP male population structure in culture ponds (the Yangtze River delta, China). Sixteen morphometric traits and four weight data were measured for each four male morphotype. Principal component and clustering analyses were conducted to investigate the morphological variation among the four morphotypes. The study of relative growth was also employed to estimate the growth patterns of body structures (dependent variables) in relation to the carapace length (independent variable). A detailed description of the cheliped’s macroscopic characteristics that differed among morphotypes was provided, which corroborated with previous studies of the species. The four morphotypes were statistically different regarding the cheliped morphology, size, and morphometric relationships and equations, indicating a considerable variation in growth among the four male morphotypes. The present results contribute to a clear understanding of the population biology of GFP and support future management and broodstock selection activities. Full article

The polychaete Hediste diversicolor is a suitable species for industrial aquaculture; however, cost-effective culture techniques need to be developed for its intensive production. The aim of this study is to evaluate the effects of worm density and substrate height and their interaction, as well as feeding frequency, on the rearing performance of H. diversicolor. Two trials were conducted. In trial 1, the effects of two substrate heights—6 and 12 cm—and two rearing densities—1000 and 4000 individuals m⁻²—were assessed in terms of worm growth and biomass production. Worm initial wet weight was 48 mg, and specimens were fed with commercial fish feed during a 70-day assay. The results show no interaction between rearing density and substrate height, and confirm density as a key factor in growth; however, a density of 4000 individuals m⁻² results in a significant increase in production (final biomass three times higher for the highest rearing density) without affecting survival. In trial 2, the effect of three levels of feeding frequency—seven days a week; three times a week; and once a week—on growth in individuals of three weight classes—small (25–50 mg); medium (100–150 mg); large (250–350 mg)—was evaluated in a 15-day growing assay. Feeding frequency showed a major influence on the smallest size class, with the best growth indicators obtained at the highest feeding frequency. This study shows that Hediste diversicolor can be reared at a high stocking density to obtain a higher biomass production, and that feeding frequency must be considered as an important factor and adapted to the culture phase. Full article

First feeding of many fish larvae depends on live feed. A comparative investigation on the effectiveness of different types of live feed is not available to our knowledge. Hence, we conducted a study to examine the effect of different types and combinations of live feed on the performance (survival rate, total length, body width, body mass, malformation rate) of pikeperch, Sander lucioperca, larvae. From day 0 (onset of exogenous feeding) to day 10, the saltwater rotifer Brachionus plicatilis, the freshwater rotifer Brachionus calyciflorus, the ciliate Paramecium bursaria, copepods (nauplii and copepodites) from a lake population, and Artemia nauplii were tested. Feeding with B. plicatilis, B. calyciflorus, and P. bursaria resulted in high survival rates of 80% and a homogenous and significant growth (increase in total length of 50% and in body width of 20%). As follow-up feed, copepod nauplii and Artemia nauplii were tested from day 11 to day 20. Copepod nauplii were superior to Artemia nauplii, as larvae fed with copepods showed higher survival rates (67–70% versus 38–47%) and a more homogeneous growth. A switch from seawater live feed to freshwater live feed or vice versa resulted in decreased survival rates. Therefore, a feeding regime consisting of B. calyciflorus or P. bursaria followed by copepods is considered optimal as first feed of pikeperch. The malformation rate was not affected by the tested feeding regimes. To investigate the wider applicability and transferability of these findings, complementary investigations were performed on burbot, Lota lota, and the freshwater whitefish Coregonus atterensis. The feeding regimes used for S. lucioperca larvae were also suitable for Lota lota. Moreover, L. lota could be fed with lake copepods from the onset of exogenous feeding. For C. atterensis, initial feeding with B. plicatilis, B. calyciflorus, or P. bursaria had no positive effects. Feeding with copepods from the onset of exogenous feeding was optimal considering survival rate and growth. Therefore, optimal first feeding regimes are very species specific and should be established for each new species. Full article

The disposal of treated and untreated sewage near shellfish harvesting areas is a global concern. Discharged sewage may be contaminated with enteric viruses present in human faeces. Bivalve molluscs, in turn, act as vectors for enteric viruses through bioaccumulation and retention of these viruses during the filter-feeding process, resulting in outbreaks of infections due to the consumption of contaminated shellfish. This review was conducted using peer-reviewed articles published from 2012 until September 2022, obtained from online databases such as Google Scholar, Scopus, and Science Direct, highlighting the challenges that the shellfish industry is faced with concerning pollutants ending up in the shellfish production areas. Developed countries have made some advancements by upgrading sewage infrastructures, which reduced viral loads in sewage. However, it is difficult to measure the significance of these improvements, as there are no regulations in place which stipulate the permissible limits for viruses. In most developing countries, including South Africa, there is a lack of effective management plans for virus monitoring in shellfish harvesting areas. The findings of this study indicated a need for extensive research on the origin of viruses, their interactions with other organisms within the marine ecosystem, the quantification of viruses within the Saldanha Bay harbour, and the development of virus management plans which currently are non-existent. Full article

Embryonic and larval development of tilapia (Oreochromis niloticus) is very vulnerable to climate change. This study was conducted for an assessment of the embryonic and larval development of Nile tilapia in traditional hatchery and re-circulatory thermostatic systems. Daily changes in embryonic and larval development were measured through microscopic observation and image analysis in the laboratory. Climatic data and water quality parameters were measured every day using appropriate devices. Water temperature was varied with room temperature at the traditional hatchery system while it was maintained at 28.50 °C in the re-circulatory thermostatic system. A total of 200 unhatched eggs were stocked in every three trays of both systems. The egg diameters of the gastrula, segmentation, and pharyngula stages were measured at higher (2261.47 ± 81.66 µm, 2646.24 ± 17.98 µm, and 2710.90 ± 16.60 µm) in the re-circulatory thermostatic system than in the traditional hatchery system (2261.07 ± 81.52 µm, 2645.47 ± 18.24 µm, and 2710.01 ± 16.45 µm), respectively. For both systems, egg colors, egg size, black pigments, germinal ring, eye shape, tail, and heartbeat were determined through microscopic observation. Higher hatching and survival rates were found under the re-circulatory thermostatic system (95% and 97%) than under the traditional hatchery system (85% and 81%). About 6 h less hatching time was required under the re-circulatory thermostatic system than under the traditional system. At the end of 30 DAH (Days After Hatching), larval length and weight under the re-circulatory thermostatic system were found to be higher (15.736 ± 0.424 mm and 0.0528 ± 0.004 g) than under the traditional hatchery system (15.518 ± 0.415 mm and 0.050 ± 0.004 g), respectively. Larval growth patterns for both systems were found to have an exponential trend. PCA analysis revealed that two components were identified, one primarily associated with morphometric characteristics and the other with climatic and water quality parameters. These components showed that there were several interrelationships between the morphometric changes and the climatic and water quality parameters. The characteristic changes of larval development under the re-circulatory thermostatic system and the traditional hatchery system were found to be remarkably similar except for some deformities denoted under the traditional hatchery system. The changes of yolk sac, body pigmentation, dorsal and caudal fin shape, eye size, and head length and width were determined from 1 DAH to 30 DAH. After absorbing the yolk sac, ready-made feed was provided. The water temperature was varied from 30.50 °C to 35.50 °C in the traditional hatchery system. The highest air temperature and humidity were 33.87 °C and 69.94% while the lowest were 29.63 °C and 45.62%, respectively, in the traditional hatchery system. There has been no such comprehensive comparative study on hatchery production in Bangladesh, and therefore, further research might be carried out on broader aspects. This research would be highly beneficial for improving seed production at the tilapia fish hatchery level in the country. Full article