Growth and reproduction aspects of Pimelodus maculatus Lacepede, 1803 , Brasil

Growth and reproduction parameters of the yellow-mandi, Pimelodus maculatus Lacepede, 1803 (Siluriformes, Pimelodidae), were determined for the Cachoeira Dourada reservoir (GO/MG). The field work occurred throughout February 2007 to January 2008 (with the exception of December 2007). Gill nets with mesh sizes from 1.5 to 10 centimeters were placed in three different areas in the reservoir and were collected 24 hours later. A total of 538 specimens were captured, amongst which 242 were females, 219 were males and 77 could not have their sex determined. Sex ratio differed from 1:1 only during July 2007 and January 2008, with males and females predominating in each of those months. Males occupied the medium length classes (18.9 to 24.3 cm) while females were most abundant in the superior classes (from 27 to 37.8 cm).The growth constant K was statistically equal for males (K=0.1851) and females (K=0.1708), however, females P. maculatus may have a greater investment in reproductive tissue, a fact indicated by the elevated values of Kn and GSI during the summer. Bearing in mind that P. maculatus reproduces in the rainy season, a greater gain in weight is expected during the months before the reproduction season, and that after it occurs the fish loses fat and weight as a consequence of metabolic effort. Still, the absence of juveniles may be an indication that the species did not find in the reservoir the proper conditions for reproduction and growth of its fry. Keywords: condition factor, GSI, length-weight relationship, Population Dynamics. O presente estudo procurou averiguar os parametros de crescimento e reproducao do mandi-amarelo, Pimelodus maculatus Lacepede, 1803 (Siluriformes, Pimelodidae), no reservatorio de Cachoeira Dourada (GO/MG). As coletas ocorreram de fevereiro de 2007 a janeiro de 2008 (exceto em dezembro de 2007), em tres pontos do reservatorio, com auxilio de baterias de redes com malhas variando de 1,5 a 10,0 cm entre nos adjacentes durante 24 horas. Foi capturado um total de 538 individuos dentre os quais 242 femeas, 219 machos e 77 de sexo indeterminado. A proporcao sexual diferiu de 1:1 em julho de 2007 e janeiro 2008, com o predominio de machos e femeas, respectivamente. Os machos concentraramse nas classes de comprimento medianas (18,9 a 24,3 cm) enquanto que as femeas nas superiores (de 27 a 37,8 cm). A constante de crescimento K foi estatisticamente igual entre machos (K=0.1851) e femeas (K=0.1708), no entanto, P. maculatus femeas pa