(Population structure aspects of the "peixe-cadela” Galeocharax knerii Steindachner, 1878) in the Bariri, Reservoir, Tietê River, São Paulo State, Brazil.)

Abstract

In this work, carried out from March, 1985 through March, 1986, 449 exemplars of "pacu", Piaractus mesopotamicus, originated from induced reproduction were utilized. Initially, 2,000 exemplars were selected and distributed into 3 masonry tanks, measuring 1,000 m², in the densities of 1 fish per 2 m² (2 tanks) and 1 fish per m² (1 tank). Monthly, 10 individuals were captured from the first two tanks and 15, from the last one and their blood was drawn in order to obtain plasma utilized in the determination of the concentrations of: glucose, total proteins, Ca^{+ +}, Na⁺ and K⁺. The mean values for each one of these variables were calculated taking into account the sex, the gonad maturation stage and the stock density. The variation spans were, for glucose: 43 to 200 mg%; for total proteins: 2.1 to 8.0 g%; for Ca⁺⁺: 5.8 to 19.0 mg%; for Na⁺: 108 to 156 meq/L and for K⁺: 2.6 to 8.7 meq/L.