Unveiling the Effect of Stocking Density and Salinity on Mucus-Associated Greenwater Qualities, Physiology, and Growth Performance of Euryhaline Milkfish Chanos Chanos

A wet laboratory experiment was carried out to evaluate the effect of Chanos chanos (Forsskal, 1775) produced greenwater under different salinities and stocking densities on growth performance, water characteristics, and microbial load. The experiment followed a 3 × 4 factorial design with three different salinities (10, 20, and 30 ppt), each with four different stocking densities (20, 40, 60, and 80 fish/tank). The C. chanos fingerlings (1.996 ± 0.14 g) were acclimatized to different salinities and distributed to 12 treatment groups in triplicates based on different stocking densities in a 500-L tank. At the end of the experiment, the average final weight, specific growth rate, FER, and PER were higher and FCR was better at 20 ppt salinity and stocking density of 20 fish/tank. Survival was not affected by the varied salinities and stocking densities. Greenwater parameters such as ammonia and nitrite values were significantly lower at 20 ppt salinity and at 20 fish/tank. Ammonia values were not significantly affected by the interaction of different salinities and stocking densities, whereas nitrite is significantly affected by the interaction in greenwater culture system. The total heterotrophic bacterial (THB) count in the culture water was lower at 20ppt salinity and 20 fish/tank, whereas the THB count of the C. chanos mucus sample was found to be at moderate count depicting less stress when fish were reared at salinity 20 ppt and 20 fish/tank. The algal density increased significantly with an increase in salinity and stocking density. To study the common bacterial diversity in the greenwater, metagenomics study of fish skin mucus was performed which provide baseline information about the potential beneficial microbial community that improves and maintains the culture environment and animal health. Overall, 20 ppt salinity and 20 fish/tank provided a suitable condition for culture without water exchange in tanks with beneficial mucus bacterial community. This study has potential application in brackishwater and inland saline aquaculture as these euryhaline fish species can be promoted in inland saline areas as climate-resilient adaptation strategies.