ABSTRACT The effect of diets with varying crude protein-to-precooked cornstarch (P:S) ratios on growth performance, feed efficiency, carbohydrase activity, and blood chemistry of juvenile Lutjanus guttatus was evaluated. Four isoenergetic (19.0 kJ g−1) diets containing different P:S ratios (46:18, 38:30, 34:35, and 31:40) were formulated to feed fish for ten weeks in triplicate. Each diet was tested in triplicate in groups of 35 fish per tank (average body weight 19.4 ± 0.3 g) to apparent satiation three times a day. The weight gain, specific growth rate, and feed conversion ratio obtained with P38S30 and P34S35 were not significantly different vs. P46S18. Survival does not present significant differences among treatments. Biological indices (condition factor, hepatosomatic index, viscerosomatic index, and intraperitoneal fat rate) showed no significant differences among treatments. Body protein content decreased significantly with increasing precooked cornstarch concentration, while body lipid levels increased. Blood chemistry values were within those of healthy juveniles, except for glucose values. An increase in pancreatic α-amylase and intestinal α-glucosidase blood chemistry values were within those of healthy juveniles, except for glucose values. An increase in pancreatic α-amylase and intestinal α-glucosidase levels concomitant with increasing precooked cornstarch concentration showed the capacity of juvenile L. gutattus to digest high precooked cornstarch levels. Growth performance, biological indices, and hematological parameters showed that L. guttatus could digest and metabolize up to 35% of precooked cornstarch through increased plasma glucose levels and the α-amylase and α-glucosidase activities. Without negative effect on growth performance.

ABSTRACT Pacific red snapper (Lutjanus peru) is an important commercial species in Mexico with great aquaculture potential; however, digestive physiology is still unknown. Therefore, the objective of the present work was to characterize the digestive proteases of L. peru juvenile using biochemical and electrophoretic techniques. Results showed a higher acid protease activity than the alkaline proteases, trypsin, chymotrypsin, and leucine aminopeptidase (LAP). The optimum temperature for acid proteases was between 30 to 40°C. Trypsin activity showed two maximum peaks of temperature (30 and 50°C), while alkaline proteases, chymotrypsin, and LAP had optimum temperatures of 50, 50 to 60, and 40°C, respectively. Moreover, the optimum pH of acid proteases was between 2 and 3. Also, alkaline proteases, trypsin, chymotrypsin showed pH optimums at pH 6, 9, and 5, respectively, although LAP showed two optimum pH values at 6 and 9. Acid protease zymogram showed three isoforms, totally inhibited by pepstatin A. Alkaline protease zymogram revealed six bands (125.4, 67.2, 57.9, 48.6, 29.8, and 26.9 kDa), which were inhibited by specific serine-proteases and metalloproteases inhibitors. In conclusion, the main digestion in L. peru depends on stomach proteases, which are characteristic of carnivorous fish, followed by intestinal digestion supported mainly by chymotrypsin.

Abstract Enormous amounts of by-products and waste are generated during the processing of seafood, sometimes representing about 65% of the raw material employed. Seafood by-products (SB) include solid waste such as skin, head, viscera, trimmings, and bones; however, liquid wastes (effluents) derived from operations such as washing, thawing, cooking and the production of fishmeal are also produced. SB contain considerable amounts of protein and others biomolecules, which has been regularly processed as food ingredients for animal nutrition. But also, sometimes SB are used as fertilizers or discarded to environment without a previous treatment. Nowadays, there is an increasing interest in adding value to the protein material within SB by improving their properties through hydrolysis and thus releasing of peptides with bioactive properties. Thus, this review aims to present an overview of the potential of SB, focused on effluents, as a source of protein hydrolysates, summarizing their methods of production, bioactive property evaluation and structural characteristics.

ABSTRACT Silicon dioxide has been used in aquaculture to increase the abundance of diatoms; however, its relationship with water quality or productive performance has not been investigated. Our study evaluated the effect of diatomite on water quality, growth performance and proximate composition of Penaeus vannamei reared in seawater (E1) and brackish water (E2) with biofloc. Two independent experiments (E1 and E2), each one with three treatments with biofloc were evaluated: treatments D with a weekly addition of diatomite (10 g m-3); the treatments D plus a continuous inoculum of diatom Chaetoceros muelleri (DD); and only biofloc like control, for E1 was used post-larvae with an initial body weight (IBW) of 0.0075 g; while in E2 was used juvenile with an IBW of 1.42 g. After seven weeks in E1, non-significant differences were registered in survival, weight gain (WG), specific growth rate (SGR) and feeding conversion rate (FCR) between DD treatment and control. However, in E2, the treatment D showed significantly higher WG (9.83 g) and SGR (4.25% d-1) compared to control (7.64 g and 3.86% d-1, respectively). Conversely, the FCR was lower in treatment D (1.16) compared to control (1.49). Non-significant differences were recorded in the proximate composition for shrimp, periphyton, and biofloc, among treatments in both experiments. Levels of nitrogenous wastes were similar among treatments. While in E2, the concentration of settleable solids was significantly higher in treatments with diatomite compared to control. Our results recommend the use of diatomite to improve the growth performance of shrimps cultured in brackish water with biofloc.

ABSTRACT The objectives of the present study were to characterize biochemically the proteases present in gastric juices from adults of the southern king crab (Lithodes santolla) and the Chilean rock crab (Cancer edwardsii), to determine the classes of proteases using specific inhibitors, as well as to evaluate the effect of temperature and pH that affect the proteolytic activity. The enzyme activity analysis revealed non-significant differences between the activities of serine proteases (trypsin and chymotrypsin) in both species. On the other hand, acid protease activity in C. edwardsii was significantly higher than in L. santolla. The activity of aspartate proteases was inhibited by Pepstatin A in both species, with no significant differences in the extent of inhibition between them. The maximal enzyme activity detected for both species occurred at alkaline pH. The optimum pH for proteolytic activity was ranged between 7 and 9 for C. edwardsii, and between 7 and 11 for L. santolla. Moreover, the highest proteolytic activity was recorded at 60°C in both species. However, at this temperature, enzyme activity was unstable after 20 min. Finally, collagenase-like activity in the gastric juices was detected for both species; this activity deserves further investigation, considering its biotechnological potential.