Optimal dietary L-glutamine level improves growth performance and intestinal histomorphometry of juvenile giant trahira ( Hoplias lacerdae ), a Neotropical carnivorous fish species

Even though glutamine is a non-essential amino acid, its inclusion in diets can be used as a tool to optimize the intestinal health and growth of fish, reason why it has been considered as a functional amino acid. Thus, the aim of this study was to evaluate the dietary supplementation with different levels of L-glutamine for juvenile giant trahira ( Hoplias lacerdae ), a Neotropical carnivorous fish species. For this purpose, a completely randomized design with six treatments (diets supplemented with 0.0; 2.0; 4.0; 6.0; 8.0 or 10.0 g/kg of L-glutamine) and five replicates was used. Five hundred ten juveniles of giant trahira (1.69 ± 0.10 g and 4.67 ± 0.10 cm) were divided into 30 circulars tanks (20 L) arranged in a water recirculating system. After 12 weeks of feeding, fish growth performance parameters (survival rate, weight and length gain, feed conversion, specific growth rate, protein efficiency ratio, length, final weight uniformity, carcass yield and intestine length), somatic indices (viscerossomatic, hepatosomatic and intestinesomatic), whole-body chemical composition and intestinal histomorphometry were evaluated. According to the polynomial regression applied, there was a quadratic effect ( p  < 0.05) of L-glutamine levels on fish weight gain, length gain and length uniformity. The L-glutamine levels that yielded the highest values for these parameters were estimated at 4.83 g/kg, 4.92 g/kg, 4.97 g/kg, respectively. Whole-body chemical composition was not affected by the L-glutamine supplementation. The villi height in the median portion and the muscular tunic thickness in the median and posterior portion of the intestine also exhibited a quadratic trend ( p  < 0.05). Furthermore, 5.42 g/kg, 5.16 g/kg and 5.21 g/kg, are the respective L-glutamine levels that maximized these metrics. It has been concluded that dietary supplementation with L-glutamine can improve growth performance and intestinal histomorphometry of juvenile giant trahira and at the same time, the optimal level in the diet is between 4.83 and 5.42 g/kg.