The effectiveness of the immune defense of Litopenaeus vannamei previously reared in biofloc or in a traditional clear seawater rearing system was assessed after a bacterial challenge with a pathogenic strain of Vibrio harveyi. The changes caused by its previous rearing system condition or the challenge were assessed in terms of metabolites (glucose, cholesterol, acylglycerides, protein), hemocyanin, the antioxidant defense system (superoxide dismutase, and catalase), and gene expression related to immune response (superoxide dismutase, alpha2 macroglobulin, prophenoloxidase, hemocyanin, and penaeidin‐3a). The biofloc rearing system was associated with a significant increase in protein, the antioxidant defense system, and the superoxide dismutase, alpha2 macroglobulin, and prophenoloxidase genes. For shrimp previously reared in biofloc, a positive interaction with the presence or absence (control) of V. harveyi significantly affected the hemocyanin concentration, and the interaction between the two rearing systems in shrimp challenged with the bacteria produced a higher transcription of the hemocyanin gene. Likewise, biofloc and clear seawater maintained a higher transcription of prophenoloxidase gene after the bacterial challenge. In the absence of the bacteria, shrimp of the biofloc group produced a higher transcription of the penaeidin‐3a gene. V. harveyi caused hepatopancreatic lesions and mortalities only in shrimp previously reared in clear seawater. These results suggest that biofloc helps to prevent the development of disease by improving the shrimp immune response.

Common snook (Centropomus undecimalis) is a marine species with high aquaculture potential; although its digestive physiology is still unknown and knowledge of that could allow the development of a balanced feed for commercial culture of this fish. The objective of this study was to partially characterize the digestive proteases in C. undecimalis using electrophoretic and biochemical techniques. A total of 50 wild snook juveniles were used to determine the optimal values of pH stability and temperature as well as the effect of inhibitors on digestive, gastric and intestinal proteases. The optimal pH for gastric proteases was obtained to be 2 with stability obtained between 2 and 8; the optimal temperature was detected at 75ºC for in vitro test, and the thermal stability was between 25 and 45ºC. Intestinal proteases showed two peaks of activity at a pH of 7 and 11; meanwhile, the greatest stability was found between a pH of 4 and 10; the optimal temperature was at 65ºC, and the greatest stability was detected between 35 and 45ºC. Up to 86% of the gastric protease activity was inhibited by pepstatin A; meanwhile, the intestinal proteases TPCK, TLCK, 1-10 Phenanthroline, SBT1, EDTA, PMSF and ovalbumin reduced the activity by 17%, 68%, 85%, 41%, 40.5%, 60% and 59%, respectively.

This study was conducted to evaluate juveniles' Ocyurus chrysurus (13.7 ± 0.45 g initial weight) to utilize lipid as an energy source on growth, feed efficiency, body composition, digestive and hepatic enzyme activities. Four diets of two protein levels (40 and 50%) with two lipid levels (6 and 12%) and 2% of digestible carbohydrates were formulated. Fish were fed for 60 days to apparent satiation at a stocking density of 10 fish per tank (100 L). Growth gain of fish fed 50% dietary protein was higher than of fish fed 40% dietary protein (P < 0.05). However, feed efficiency was significantly higher at 12 than 6% of dietary lipid. Whole-body lipid and glycogen in the liver increased dramatically with dietary lipid content-alkaline protease activity trend increased as dietary protein increased. Trypsin activity increased significantly as dietary lipid decreased, whereas chymotrypsin activity showed the opposite trend (P < 0.05). Bile salt-dependent lipase activity trend towards increasing as dietary energy decreased. Glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), and fructose-1, 6-biphosphatase (FBPase) significantly increased with increasing dietary lipid levels. However, alanine aminotransferase (ALT) activity increased with dietary protein content. On the other side, pyruvate kinase (PK) activity increased with both dietary protein and lipid content. This study indicates that high dietary lipid (12%) improved the feed efficiency but did not reduce dietary protein demand in juveniles O. chrysurus.

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