Effect of water temperature and prey concentrations on initial development of Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae), a freshwater fish

The aim of this study was to investigate the effects of water temperature and prey concentrations (Artemia nauplii) on the initial development of Lophiosilurus alexandri larvae. The experiment was conducted using a 4 x 2 factorial design, with four water temperatures (23, 26, 29 and 32 °C), two different initial prey concentrations (P700 and P1,300) and three replicates. Feeding was increased during the fifteen-day experiment. At the end of the experiment, the survival and condition factor were affected only by prey concentrations, with elevated numbers of Artemia nauplii leading to higher averages of these variables. The total length (TL) and specific growth rate were separately influenced by temperature and prey concentration, without interaction between them, and weight showed an interaction with these factors. In general, an increase of temperature (23 to 32 °C) improved the growth and nitrogen gain in L alexandri larvae. For TL, the optimal temperatures estimated were 31.4 and 31.0 °C for P700 and P1,300, respectively. Similar mean body weight larvae and nitrogen gain were observed at 23 °C for both levels of prey concentrations. For other temperatures, the P1,300 level provided greater weight gain for L. alexandri. Therefore, it is suggested that temperatures between 29-32 °C combined with a higher level of prey concentration maximise the development and nitrogen gain in L. alexandri larvae. Moreover, this is the first result about nitrogen incorporation in neotropical fish larvae. O objetivo deste estudo foi investigar os efeitos da temperatura da água e concentrações de presas (náuplios de Artemia) no desenvolvimento inicial de larvas de Lophiosilurus alexandri. O experimento foi conduzido em esquema fatorial 4 x 2, com quatro temperaturas da água (23, 26, 29 and 32 °C), duas concentrações de presas (P700 e P1.300) e três réplicas. A quantidade de alimento ofertado aumentou durante os 15 dias de experimento. Ao final do experimento a sobrevivência e o fator de condição foram afetados apenas pela concentração de presas, sendo que a maior concentração proporcionou médias superiores para as variáveis mencionadas. O comprimento total (CT) e a taxa de crescimento específico foram influenciados separadamente pelos fatores temperatura e concentração de presa, sem interação entre os fatores, e o peso individual das larvas apresentou interação entre os fatores estudados. Em geral, o aumento da temperatura (de 23 para 32 °C) promoveu o crescimento e o ganho