This study aimed to investigate stocking density during larviculture of Colossoma macropomum in recirculating aquaculture system with slightly saline water. Densities of 10 (D10), 30 (D30) and 50 (D50) larvae/L were tested with five replicates each. Larvae were fed with Artemia nauplii during the first 15 days and with commercial diet from day 16 to day 30. Water was maintained at a salinity of 2.01 ± 0.41 g of salt/L, and performance and survival were evaluated throughout the experiment. At the end of the experiment, larvae of each tank were classified according to size as small—S (<18.0 mm and <0.08 g), medium—M (>18.0 mm and <22.2 mm, >0.08 g and <0.15 g) and large—L (>22.2 mm and >0.15 g), and the size distribution was calculated for each stocking densities evaluated. Larval weight, length and specific growth rate were not affected by the tested stocking densities throughout the experiment (p > .05). Heterogeneity was recorded at 30 days of larviculture for all tested densities with a predominance of class M animals. Survival during feeding with Artemia was not affected by the tested densities (p > .05). Survival during feeding with commercial diet was highest for D10 and lowest for D30 (p < .05). Global survival, considering the experiment as a whole, was similar among the tested stocking densities (p > .05). Larviculture of C. macropomum can be successfully carried out at stocking densities of up to 50 larvae/L during the first 30 days of rearing in slightly saline water in recirculating aquaculture system.

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This study aimed to evaluate sexing techniques for juvenile Lophiosilurus alexandri. With this aim, we evaluated three techniques: coelioscopy, performed with the use of video surgery equipment; coeliotomy, a surgical procedure for direct visualization of the gonads; and sex determination using a urethral probe to compare the genital papillae. For coelioscopy, the survival rate was 100% 30 days after the procedure, and the fish restarted eating 10 days after surgery. This technique resulted in a 100% correct identification of individuals identified as females, whereas for males, it was 66.6%. There was no significant difference between males and females for anesthesia induction and recovery times. However, the procedure took longer for males because of the difficulty in observing the gonads, which can be attributed to the large amount of visceral fat in males. Coeliotomy also resulted in a 100% survival rate 30 days after surgery, and the efficiency of this technique was 96.3% for males and 93.9% for females. The fish restarted eating between 10 and 14 days after surgery, and there were no significant differences between males and females for anesthesia induction and recovery times for the surgical procedure to visualize the gonads (P > 0.05). The urethral probe technique was less efficient with an accuracy rate of 67.8% and 81.8% for males and females, respectively. We conclude that coeliotomy was more efficient for sexing both sexes of juvenile L. alexandri.

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