A 52-day experiment was conducted to determine the crude protein (CP) requirements of juvenile matrinxã Brycon amazonicus, and to evaluate their resulting growth performance, hematological parameters and enzymatic activities. Sixty fish (29.03g ± 1.16g) were distributed in 12 tanks (310 L) with a completely randomized design, and maintained at four dietary crude protein levels (270, 320, 350, 390 g.kg-1) for 52 days. The results revealed that the fish fed diet 390 g.kg-1 CP had the best final weight, weight gain, feed conversion ratio, specific growth rate, protein efficiency ratio and lipid retention rate. The same could be stated for hematocrit, number of circulating erythrocytes, triglycerides and total proteins of the hematological profile (p<0.05). In the whole body composition, dry matter content was lower in the fish fed 390 g.kg-1 CP, while lipid content was higher in the fish fed 350-390 g.kg-1 CP (p<0.05). No differences were observed in CP and ash (p>0.05), or in the activities of digestive enzymes (p>0.05). In short, our findings suggest benefits of the 390 g.kg-1 CP feed for being the most adequate for this species’ juvenile stage.

The recent availability of commercial platforms for behavioral analysis in zebrafish larvae based on video-tracking technologies has exponentially increased the number of studies analyzing different behaviors in this model organism to assess neurotoxicity. Among the most commonly used assays in zebrafish larvae are basal locomotor activity (BLA) and visual motor response (VMR). However, the effect of different intrinsic and extrinsic factors that can significantly alter the outcome of these assays is still not well understood. In this work we have analyzed in 143 larvae the influence of age (5-8 days post-fertilization), time of day (8:00, 10:00, 12:00, 14:00; 16:00, 18:00, and 20:00 h), and experiment (three experiments performed at different days) on BLA and VMR results (4,004 analyses for each behavior). Results from both behaviors were adjusted to a Random-Effects linear regression model using generalized least squares (GLS), including in the model the effect of the three variables, the second-way interactions between them and the three-way interaction. The results presented in this manuscript show a specific effect of all three intrinsic factors and their interactions on both behaviors, supporting the view that the most stable time period for performing these behavioral assays is from 10:00 am to 04:00 pm, with some differences depending on age of the larva and the behavioral test.