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In this study, a biofloc technology (BFT) based 90‐day feeding trial was performed to estimate the effects of four different dietary protein levels (290, 320, 350 and 380 g protein kg−1 diet; 29P, 32P, 35P, and 38P, respectively) on growth performance, digestive enzyme activity, non‐specific immune response, whole‐body proximate and fatty acid composition and intestinal microbiota of Farfantepenaeus aztecus. Final weight, weight gain, and specific growth rate improved with protein levels up to 35P per kg of diet, below which decreased significantly. Significant differences were observed in total hemocyte count, acid phosphatase, respiratory burst, glutathione, alkaline phosphatase, and total antioxidant capacity indices of shrimp fed different dietary protein levels. Protease, lipase, and amylase activities of shrimp were also affected by dietary protein levels. Proteobacteria was the most abundant bacteria among the groups. Overall, this study revealed that using 35% dietary protein is optimal in F. aztecus culture under environmentally friendly BFT conditions. Furthermore, these results provide a theoretical basis for future research on the evaluation of functional ingredients in diet for more economical production of F. aztecus at optimal protein levels. [ABSTRACT FROM AUTHOR]

Cryptocaryoniasis remains a major parasitic disease and economic challenge for marine aquaculture. Cryptocaryoniasis in marine fish is caused by Cryptocaryon irritans (Ciliata). A theront is a motile, free‐swimming stage in the life cycle of C. irritans, which is typically the infective stage that actively seeks out a host to initiate infection. Population density and growth rate of theronts were investigated in Nile tilapia, Oreochromis niloticus fed with citric acid‐supplemented feed. The experiment involved feeding three diets with graded levels of citric acid (0, control diet, 0.5, 1 and 1.5 g kg−1 diet), to seawater‐adapted Nile tilapia (O. niloticus) juveniles for 21 days. The results showed that citric acid in the fish feed had an impact on the theront number of C. irritans in a manner of dose‐dependent. In the experimental cohort administered a diet supplemented with 1.5 g kg−1 citric acid, the population density of theronts was observed to be significantly reduced, measured at 29 ± 3.34, as opposed to 473.34 ± 16.48 in the control group at the culmination of the experiment. The observed population growth rate of theronts was significantly higher in the control group than in the group administered the citric acid feed (p <.005). The growth rate (r d−1) was 0.12 in control, 0.05 in 0.5 g kg−1, 0.031 in 1 g kg−1, and − 0.031 in 1.5 g kg−1 citric acid‐supplemented groups. Fish growth and feed conversion ratio were not affected by the citric acid in the feed. In conclusion, the findings of this investigation provide a valuable addition to our understanding of the potential protective effects of citric acid supplementation for fish against the C. irritans parasite. This is evidenced by the observed reduction in theronts present in the water. [ABSTRACT FROM AUTHOR]

Hysterothylacium aduncum is a parasitic nematode that infects mainly marine fish. The information on the heterogeneity in the aggregation of macroparasites in fish species is still limited, particularly for the Raphidascarid nematode H. aduncum that infects exploitable marine fish species including horse mackerel (Trachurus trachurus). This study aimed to investigate the heterogeneity of the distribution of H. aduncum to better understand macroparasite aggregation in marine fish. Weibull tests comprising Maximum likelihood were used to analyze the frequency distribution of parasites within a fish host population over the three years period. The parasite, H. aduncum (third larval stage) prevalence was found to be 88% and the condition factor was 1.30∓0.029 in un-infected fish and 1.12∓0.022 in infected fish. The clustered pattern was observed in H. aduncum in horse mackerel. The relation between parasite load and the fish condition factor was found to be significant and conformity of length and weight was affected by parasite load. It is the first time that aggregation has been observed in H. aduncum distribution and forecasts of nematode intensity in horse mackerel. The findings related to the large individual variations suggest that this pattern is significant and should be considered for host-parasite dynamics. [ABSTRACT FROM AUTHOR]