Abstract:The application of β-1,3/1,6-glucan derived from yeast at five concentrations (0%, 0.5%, 1.0%, 1.5%, and 2.0%) in formulated diets was evaluated in juveniles for its effects on the growth, survival, digestive enzymatic activity, and expression of genes associated with the immune system (interlukin-10 (IL-10), transforming growth factor (TGF), occludin (OCC), mucin2 (MUC2), lysozyme (LYS), and nucleotide-binding and oligomerization domain 2 (NOD2)) in tropical gar (Atractosteus tropicus). For the experiment, three replicates of 30 fish per experimental unit (70 L) were cultivated for 62 days. The growth results showed no statistically significant differences in relation to weight and total length between treatments. The activity of digestive enzymes (alkaline proteases, trypsin, leucine aminopeptidase, and amylase) did not show significant differences between treatments, except for chymotrypsin activity, where fish fed 1.0% and 1.5% of β-glucans showed higher activities compared with the rest of the treatments. On the other hand, the analysis of gene expression did not show significant differences between treatments, although a tendency of increase in the expression of IL-10, TGF, MUC2, and OCC was observed with an addition of 1.5% of the prebiotic, but there was a decrease in the fish fed with 2% of the prebiotic. It is possible to include concentrations of between 0.5% and 1.5% of β-glucans in the diets for A. tropicus, with no detectable adverse effects on growth, survival, digestive enzyme activity, or specific gene expression. β-glucan 1,3/1,6 added at 1.0% and 1.5% in the diet significantly increases chymotrypsin activity.

El diseño de dietas con base en la fisiología digestiva, así como un adecuado esquema de alimentación, per- miten la disminución del canibalismo y el incremento de la supervivencia en la etapa larvaria de peces. Por lo anterior, el objetivo fue evaluar el crecimiento, supervivencia y canibalismo en la larvicultura del pejelagarto (Atractosteus tropicus Gill) bajo cuatro esquemas de alimentación: CT (co-alimentación con nauplio de Artemia por 10 días y dieta comercial de trucha), T1 (alimentación con la dieta comercial de trucha desde la apertura de la boca), T2 (co-alimentación con nau- plio de Artemiay dieta diseñada para larvas de A. tropicus por 10 días) y T3 (alimentación con la dieta diseñada para A. tropicus desde la apertura de la boca), así como determinar la correlación entre el canibalismo y la supervivencia mediante un modelo de regresión lineal. Los mejores crecimientos y supervivencias se obtuvieron en los tratamientos T2 y CT. En todos los tratamientos se presentó canibalismo, siendo más alto cuando no se co-alimentó con nauplio de Artemia (T1 y T3). Se encontró una fuerte correlación (r = -0.88, p < 0.05) entre la supervivencia y el canibalismo, lo que demuestra que el canibalismo tiene efecto sobre la supervivencia. El tratamiento T2 representa la mejor alternativa para la larvicultura de A. tropicus, con mayor crecimiento y menor canibalismo.

Five experimental diets with different carbohydrates/lipid ratio (CHO:L, 0.75, 1.28, 2.10, 2.52, 4.63) were formulated. Fish were randomly assigned by triplicate (10 fish per tank, 0.50 ± 0.01 g). Growth was registered every 15 days until end of the experiment (45 days). Samples were taken for analysis of chemical carcass composition, blood chemistry, glycogen and lipid liver content, digestive and metabolic enzyme activities. Results showed that survival, growth performance parameters and plasma glucose were not affected by treatments (p > 0.05). Lipids of carcass and liver, as well as triglycerides and plasma cholesterol increase significantly as CHO:L ratio decreased. While an inversely proportional tendency was observed for carcass protein and liver glycogen (p < 0.05). Digestive enzymes did not show significant differences among treatments (p > 0.05). Finally, Hexokinase (HK), glucokinase (GK), phosphoenol pyruvate carboxykinase (PEPCK) and fructose‐1,6‐biphosphase (FBPase) showed high regulation by carbohydrates up to the CHO:L ratio of 2.10 (p < 0.05), while pyruvate kinase (PK) activity was not significantly affected by the CHO:L ratio. By the other side, glucose‐6‐phosphate dehydrogenase (G6PD) tends to significantly increase as the CHO:L ratio increases. We conclude that A. tropicus fry have a high capacity to utilize carbohydrates substituting lipids as energy source in balanced diets.

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Four microencapsulated diets were evaluated with respect to the growth and survival of tropical gar Atractosteus tropicus larvae. The treatments consisted of four experimental diets and one control diet 1) fish meal, 2) a combination of pork and poultry meals, 3) Nannochloropsis gaditana meal, 4) enzyme preparation and the control treatment 5) Artemia nauplii. The evaluation indicated that the larvae fed the Artemia nauplii obtained the greatest growth and survival (3.93 cm, 0.19 g y 82 % respectively), which justifies a correct culture system operation. While larvae fed microencapsulated diets best values in survival were observed with diets Nannochloropsis gaditana and enzyme preparation (20.0 and 19.2 %). Our results showed that microencapsulated could be used to feed A. tropicus in feasibly form. However, more information concerning to optimize the design and manufacturing are required to improve the growth and survival of organisms.

Supplementary fructooligosaccharides (FOS) were evaluated on growth, survival, gut morphology, digestive enzyme activity and expression of intestinal barrier genes in tropical gar (Atractosteus tropicus). Four treatments were designed to include FOS (5, 10, 15 and 20 g/Kg) and were compared with a control (0 g/Kg) and the current commercial trout diet. Ten fish were stocked (0.25 ± 0.01 g and 4.2 ± 0.4 cm total length) per experimental unit by triplicate in a 45-day experiment. Fish fed with 5 and 10 g/Kg of FOS had the highest average weight and total average length. Fish fed 5 g/Kg FOS showed the best growth indexes (absolute weight gain: 2.16; specific growth rate: 4.96; and feed conversion rate: 1.23) and survival (96.66%) and also had the highest acid protease, chymotrypsin and leucine aminopeptidase activities. Fish fed 5 g/Kg FOS had a high absorption area and accumulation of lipids in the liver. Finally, relative overexpression of occluding (occ), nucleotide-binding oligomerization domain-2 (nod2) and mucin 2 (muc2) was detected in fish fed 10 and 15 g/Kg FOS. The supplementation between 5 and 10 g/Kg FOS in diets for A. tropicus juveniles could be beneficial for growth, digestive enzyme activities, gut morphology and intestinal barrier function.

For the commercial culture of the three‐spot cichlid (Amphilophus trimaculatus), it is important to have available a set of protein and lipid ingredients suitable for feed manufacturing, which allow to optimize the culture at affordable costs. The in vitro digestibility was evaluated with pH‐stat technique, using stomach and intestine multi‐enzymatic extracts from A. trimaculatus juveniles. The digestion of protein ingredients was taken place both in acid and in alkaline conditions, quantifying the total of free amino acids at the end of the hydrolysis, whereas the digestion of lipid ingredients was taken place only in alkaline conditions. The digestive enzymes of this species showed a better affinity to raw materials of animal origin such as beef meal, fish meal and premium chicken meal, which presented better digestibility. The best lipid ingredient that could be used is the fish oil. However, it is possible to use ingredients from the plant sources, such as soy or cereals, and vegetable oils such as olive, corn or soy oil. It is necessary to complement this study in vitro with the digestibility analysis in vivo, in order to determine the inclusion percentages in feeds and costs and therefore to develop an efficient feed formulation for the aquaculture of A. trimaculatus.

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