Effects of feeding levels and types of preys on growth and survival of "curimbata" Prochilodus scrofa (Steindachner, 1881) larvae fed Brachionus plicatilis and natural zooplankton

Growth and survival of curimbata Prochilodus scrofa larvae were examined in the laboratory in relation to three feeding levels, during three experimental periods lasting 21 days each one. The inicial daily rations consisted of 300 (R1 and PS1), 450 (R2 and PS2) and 600 (R3 and PS3) organisms.larva super(-1).day super(-1) of the rotifer (R) Brachionus plicatilis and wild zooplankton (PS). Mean survival rates of the R larvae were high (more than 60%) and not related to feeding levels, although these levels influenced the larval growth. This influence was more evident in the treatments with the lowest survival rates and the highest prey densities which corresponds to R3 treatments of the 1st and 3rd periods. Among the larvae fed wild zooplankton, those of the 1st period showed considerably lower mortality than those of the 2nd and 3rd ones and it seems to be related to the diversity of the zooplankton composition offered to the larvae in that period, which was constituted mainly of Brachionus sp. rotifers. This fact suggests that "curimbata" larvae may be selective predators, at least for the first days of exogenous feeding.Original Abstract: O crescimento e a sobrevivencia de larvas de curimbata Prochilodus scrofa foram examinados, em laboratorio, por 3 periodos experimentais com duracao de 21 dias cada, em relacao a alguns niveis de alimentacao. As quantidades diarias iniciais, ate o 4 dia de alimentacao, foram de 300 (R1 e PS1), 450 (R2 e PS2) e 600 (R3 e PS3) organismos.larva super(-1), divididas em duas refeicoes, utilizando-se como alimento o rotifero (R) de agua salobra Brachionus plicatilis cultivado em massa, e o zooplancton natural (PS) coletado em tanques previamente fertilizados. A partir do 5 dia, tais quantidades foram duplicadas. Para ambos os tipos de alimento, os niveis iniciais de alimentacao nao influenciaram as taxas de sobrevivencia. As taxas medias de sobrevivencia obtidas com o alimento R, nos 3 periodos experimentais, foram elevadas (acima de 60%), independentemente da quantidade inicial de organismos oferecidos. Por outro lado, os niveis de alimentacao influiram no crescimento das larvas e essa acao foi mais acentuada nos tratamentos onde se observaram menores taxas de sobrevivencia associadas aos maiores niveis de alimentacao (R3 do 1 e 3 periodos). Para as larvas alimentadas com o zooplancton selvagem (PS), as taxas medias de sobrevivencia foram bastante similares entre os niveis PS1, PS2 e PS3. Por outro lado, foram muito superiore