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.