Effects of impoundment on the body condition of fish in the Manso reservoir, Mato Grosso State, Brazil

AIM: This study evaluated the body condition de Acestrorhynchus pantaneiro, Auchenipterus osteomystax, Pimelodus maculatus, Psectrogaster curviventris and Schizodon borellii in the Manso reservoir, Mato Grosso State, Brazil, during the first years after its formation (years I, II, III and IV). We hypothesized that sudden environmental changes alter differently the body condition, according to the time (sampling years) and sex of individuals. Also, we checked the influence of the amount of food ingested and the reproductive status on nutritional status of the species. METHODS: The body condition (Kn), the feeding activity (SRI) and reproductive (GSI) were calculated only for adults. The difference between the sampling years and sexes (used as factors) was assessed using the nonparametric Kruskal-Wallis test. Temporal influence was tested by Spearman correlation and the interaction between both factors by PERMANOVA. RESULTS: The values of the Kn showed two groups: group 1: species whose body condition decreased in the year II, with a posterior increase (A. pantaneiro, P. curviventris and S. borelli), considered sensitive to the reservoir filling; group 2: species whose body condition increased in the year II (A. osteomystax and P. maculatus), indicating a more rapid adaptation to new environmental conditions. Still, all parameters investigated were somehow affected by the dam, mainly the body condition and gonadosomatic index for several species. On the other hand, the least affected factor was the feeding activity. CONCLUSIONS: The results did not evidence a same pattern of either increase or decrease of body condition for all species examined, since everything indicates that responses are species-specific. Even with a lack of consistency in some results, we can draw some suggestions for future investigations. Responses to these questions will certainly contribute to aggregate data to help better explain the body condition of fish species in dammed environments. OBJETIVO: O objetivo deste estudo foi avaliar a condição nutricional de Acestrorhynchus pantaneiro, Auchenipterus osteomystax, Pimelodus maculatus, Psectrogaster curviventris e Schizodon borellii no reservatório de Manso, MT, Brasil, durante os primeiros anos após a sua formação (anos I, II, III e IV). Partimos da premissa que, mudanças ambientais repentinas alteram de forma diferente a condição nutricional, de acordo com o tempo e o sexo dos indivíduos. Nós predizemos também que a quantidade de ali