ABSTRACT This study aimed to evaluate the effect of using different concentrations (5, 7.5, 10, and 12.5%) of two permeating cryoprotectants, dimethyl sulphoxide (DMSO) and methanol, on Prochilodus lineatus embryos while being subjected to cooling for 2, 4, 6, and 8 h at 4 °C. We analyzed the hatching rate, viable larvae, and counts of hatched and spoiled eggs and those that did not complete their development after cooling. We observed a significant interaction among variables, permeable cryoprotectant concentration, and cooling time, having the increase of these factors caused a reduction in hatching rate. The curimba embryos showed a higher sensitivity to cold at a temperature of 4 °C for 6 and 8 h, directly influencing the production of viable larvae. We did not observe a significant difference in the variables analyzed when comparing the cryoprotectant solutions containing DMSO, methanol, and solutions containing only water and sucrose (0.5M). An increase in the concentration of cryoprotectant and cooling time promotes a reduction in the hatching rate and in the percentage of viable curimba larvae.

Resumo: O objetivo deste trabalho foi determinar o efeito do fotoperíodo sobre o canibalismo, o crescimento e a composição corporal de juvenis de trairão (Hoplias intermedius). Um delineamento inteiramente casualizado foi empregado, com quatro fotoperíodos - 0L:24D, 6L:18D, 12L:12D e 18L:6D horas de luz (L) por horas de escuridão (D) - e quatro repetições, pelo período de 90 dias. Os parâmetros analisados foram: canibalismo, crescimento em peso e comprimento, consumo alimentar, conversão alimentar, taxa de eficiência proteica, crescimento muscular e composição corporal (umidade, lipídios, cinzas e proteína bruta). Os peixes do fotoperíodo 12L:12D apresentaram maior taxa de sobrevivência e nenhum canibalismo, bem como grande uniformidade nos valores de comprimento e massa ao final do experimento. O melhor fotoperíodo para juvenis de trairão é 12L:12D, uma vez que os peixes mostraram uniformidade de crescimento e nenhum canibalismo, enquanto peixes dos grupos 6L:18D e 18L:6D apresentaram maior diâmetro de fibras musculares brancas e maior frequência de fibras de maior diâmetro. Os peixes apresentaram menor valor de lipídios no fotoperíodo 6L:18D, e o maior valor no 12L:12D. O fotoperíodo afeta a sobrevivência e o canibalismo; quanto à composição corporal, somente os lípidos são influenciados pelo fotoperíodo.

Abstract: The objective of this work was to determine the effect of photoperiod on the cannibalism, growth, and body composition of giant trahira (Hoplias intermedius) juveniles. A completely randomized design was employed, with four photoperiods - 0L:24D, 6L:18D, 12L:12D, and 18L:6D, hours of light (L): dark (D) - and four replicates, for a period of 90 days. The analyzed parameters were: cannibalism, growth in weight and length, food consumption, feed conversion, protein efficiency rate, muscle growth, and body composition (moisture, lipid, ash, and crude protein). Fish from the 12L:12D photoperiod showed the highest survival rate and no cannibalism, as well as a great uniformity for length and mass values at the end of the experiment. The best photoperiod for giant trahira juveniles is 12L:12D, as these fish showed growth uniformity and no cannibalism, while fish from the 6L:18D and 18L:6D groups had a greater diameter of white muscle fibers and a higher frequency of greater diameter fibers. Giant trahira showed the lowest value for lipids at 6L:18D and the highest value at 12L:12D. Photoperiod affects survival and cannibalism; regarding body composition, only lipids are influenced by photoperiod.