Tropical gar, Atractosteus tropicus, is a carnivorous fish species from Southern México with high value and acceptance in local markets. Therefore, the present study aims to spare proteins in diets for larviculture of this species. An experiment was performed using three different experimental diets with increasing carbohydrate levels based on potato starch (S) and decreasing protein content (P) and total energy: 16% S (16% S-44% P), 22% S (22% S-40% P) and 28% S (28% S-36% P). Tropical gar larvae (five days post-hatching, 2.1 mm average notochordal length) were assessed for growth, survival, degree of cannibalism, and digestive enzyme activities for 30 days. Highest growth and survival (24%), as well as the lowest cannibalism (33%), was seen in larvae fed the 28% S diet, and these larvae also had the highest lipase, amylase and glucosidase activities (0.28, 0.56 and 0.11 units, respectively). Protease activity (alkaline protease, trypsin, chymotrypsin, and leucine aminopeptidase) was higher in the larvae fed the 22% S diet than in those given the 16% S and 28% S diets. In conclusion, dietary inclusion of potato starch at 28% S enhanced growth, survival and some digestive enzyme activities, and decreased cannibalism in the larval gar. Potato starch could replace dietary protein as a major source of energy for A. tropicus larvae, thereby reducing the cost of diets.

The aim of this study was to compare in vitro protein digestibility between two groups of fish, at early (21 g) and late stages (400 g) of spotted rose snapper Lutjanus guttatus, to evaluate the degree of hydrolysis (DH) and total amino acid release (TAAR) using crude extracts from stomach, pyloric caeca and intestine of 13 protein ingredients including marine, animal and plant meals. Degree of hydrolysis and TAAR were measured by a pH-Stat method, and the PAGE-Zymogram was also used as complementary technique. Differences in DH were found between both grow-out stages mainly in the alkaline hydrolysis phase. Fish and squid meals (marine sources) had the highest DH and TAAR, followed by porcine meat and poultry meal byproducts from recycling sources, and soybean and canola meals (plant sources), which represent better protein sources for use in practical diets. Stomach zymograms showed two pepsin isoforms in both grow-out stages. Pyloric caeca and intestine zymograms showed five bands with proteolytic activity in the early grow-out stage, whereas four additional bands were found in late grow-out stage. Alkaline proteases were identified as serine and metalloproteases. Thus, L. guttatus presents an ontogenetically differentiated digestive enzyme pattern that modifies the DH and TAAR of different protein sources. K E Y W O R D Salkaline proteases, amino acids, electrophoresis, Lutjanus guttatus, pepsin, pH-Stat

The genus Oreochromis is among the most popular of the tilapiine cichlid tribe for aquaculture.However, their temperature and hypoxia tolerance, if tested at all, is usually tested at temperatures of 20-25 C, rather than at the considerably higher temperatures of 30-35 C typical of tropical aquaculture. We hypothesized that both larvae and adults of the heat and hypoxia-adapted Tabasco-line of the Nile tilapia Oreochromis niloticus would be relatively hypoxia-tolerant. Oxygen consumption rate ( _ MO 2 ), Q 10 and aquatic surface respiration (ASR) was measured using closed respirometry at 2 (c. 0.2 g), 30 (c. 2-5 g), 105 c. (10-15 g) and 240 (c. 250 g) days of development, at 25 C, 30 C and 35 C. _ MO 2 at 30 C was inversely related to body mass: c. 90 μM O 2 g −1 /h in larvae down to c. 1 μM O 2 g −1 /h in young adults. Q 10 for _ MO 2 was typical for fish over the range 25-35 C of 1.5-2.0. ASR was exhibited by 50% of the fish at pO 2 of 15-50 mmHg in a temperature-dependent fashion. However, the largest adults showed notable ASR only when pO 2 fell to below 10 mmHg. Remarkably, p crit for _ MO 2 was 12-17 mmHg at 25-30 C and still only 20-25 mmHg across development at 35 C. These values are among the lowest measuredfor teleost fishes. Noteworthy is that all fish maintain equilibrium, ventilated their gills and showed routine locomotor action for 10-20 min after _ MO 2 ceased at near anoxia and when then returned to oxygenated waters, all fish survived, further indicating a remarkable hypoxic tolerance. Remarkably, data assembled for _ MO 2 from >30 studies showed a > x2000 difference, which we attribute to calculation or conversion errors. Nonetheless, p crit was very low for allOreochromis sp. and lowest in the heat and hypoxia-adapted Tabasco line. K E Y W O R D Shypoxia tolerance, _ MO 2 , Oreochromis, oxygen consumption, Tabasco-line tilapiadevelopment

Partial characterizations of digestive proteases were studied in three life stages of spotted rose snapper: early (EJ), middle (MJ) and late juvenile (LJ) with corresponding average weights of 21.3 ± 2.6 g (3 months after hatching, MAH), 190 ± 4.4 g (7 MAH), and 400 ± 11.5 g (12 MAH). At sampling points, the digestive tract was dissected into the stomach (St), pyloric caeca (PC), and the intestine in three sections (proximal (PI), middle (MI) and distal intestine (DI)). The effect of pH and temperature and specific inhibitors were evaluated for acid and alkaline proteases. Total acid and alkaline protease activity showed a tendency to increase with juvenile life stage of fish while trypsin activity decreased. Differences were found in acid and alkaline protease activities at different pH and temperatures during juvenile stages. Pepstatin A inhibited total activity in the stomach extract in all juvenile stages. Activity in total alkaline protease inhibition was significantly higher in EJ using TLCK, PMSF, SBTI, Phen and Ovo than in MJ and LJ, while no significant differences were found with TPCK inhibition. Therefore increases in protease activities with fish growth through juvenile stages in which a substitution or diversification in the type of alkaline enzymes exist. These results lead a better comprehension of changes in digestive potential of Lutjanidae fish.

Studies on the nutrition of wild populations of freshwater prawns, valuable in the determination of feeding habits and requirements, are scarce or inadequate. We analyzed the digestive tract of individuals of Macrobrachium tenellum (Smith, 1871) (Palaemonidae) sampled from three different coastal habitats (an estuary, a lagoon, and a river) in the southeastern Mexico Pacific coast to determine if individuals show any variations in their enzymatic activities. Prawns of different size (adult or juvenile) showed the most significant differences among them in the kind and amount of enzyme activity, whereas location and sex differences resulted in less significant differences. Results suggest that feeding habits and not habitat, are the main cause of differences between age classes.

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A total of 300 Centropomus undecimalis juveniles, with an average initial weight of 3.16 0.28 g and average total length of 7.17 0.22 cm, were reared for eight weeks using a recirculating system to determine the dietary protein requirement for their growth and survival. The eect of ve experimental diets containing 40, 45, 50, 55 and 60% total protein content and two salinities (brackish water, BW at 5 UPS and marine water, MW at 36 UPS) were assessed. Fish were fed ve times per day at 2.5% of total biomass. All treatments were performed in triplicate,recording the individual weight and total length every 15 d, while weight gain and daily growth rate were recorded at the end of the experiment. Mean weight increased proportionally as protein content increased, with the greatest growth occurring with a 60% protein diet for sh reared in brackish water, and 55% for sh in marine water. We consider that the protein requirement in C. undecimalisjuveniles is high; in addition, it differs depending on the salinity, </

In fishes, trypsins are adapted to different environmental conditions, and the biochemical and kinetic properties of a broad variety of native isoforms have been studied. Proteolytic enzymes remain in high demand in the detergent, food, and feed industries; however, our analysis of the literature showed that, in the last decade, some fish trypsins have been studied for the synthesis of industrial peptides and for specific biomedical uses as antipathogenic agents against viruses and bacteria, which have been recently patented. In addition, innovative strategies of trypsin administration have been studied to ensure that trypsins retain their properties until they exert their action. Biomedical uses require the production of high-quality enzymes. In this context, the production of recombinant trypsins is an alternative. For this purpose, -based systems have been tested for the production of fish trypsins; however,-based systems also seem to show great potential in the production of fish trypsins with higher production quality. On the other hand, there is a lack of information regarding the specific structures, biochemical and kinetic properties, and characteristics of trypsins produced using heterologous systems. This review describes the potential uses of fish trypsins in biomedicine and the enzymatic and structural properties of native and recombinant fish trypsins obtained to date, outlining some prospects for their study.