Certificado de vigor físico para o tambaqui (Colossoma macropomum, Cuvier 1818)

Abstract

At least 64 fish species are reared in Brazil, and the major ones raised in the north are tambaqui (Colossoma macropomum), matrinxã (Brycon amazonicum), and pirarucu (Arapaima gigas). Tambaqui is by far the most studied fish species, as a consequence of its great demand and high revenue. Tambaqui is successfully raised in Brazil, Ecuador, Panama, Peru, Venezuela and Colombia. One of the main problem related to the farming of this species is the high mortality caused by handling stress and inadequate transport. The physiological answers of the organism to the stress are countless and they depend on the type and on the intensity of the stress agent. The swimming performance (Ucrit) of the fish is directly related to its capacity to transfer oxygen and energy molecules to the muscles, and at the same time, to eliminate the undesirable by-products. The Ucrit measure of farming and ornamental fish can be used as a useful stress indicator, with the advantage of being a non invasion method, of relative low cost and easy verification. The fish lots could be accompanied and, if considered weakened, they should neither be marketed nor be handled, until that normal physiological state be reestablished. This work demonstrated that previous exposure of tambaquis to hypoxia, reduced its Ucrit due to lactate accumulation in their muscles, and a period of 96 hours of recovery was not enough to reestablish the Ucrit and normal metabolism. Nevertheless, exposure to low pH and gaseous ammonia didn t cause lactate accumulation, but they reduced Ucrit of the tambaquis due to loss of plasma sodium, with consequent hemoconcentration and decrease of the aerobic capacity. The difference is the neurotoxic effect of ammonia, wich in a second moment affect muscular contraction of the fish. In both cases, a period of 96 hours of recovery was enough to reestablish the Ucrit and normal matabolism. Based on the stress situations used in this study, it is suggested that the minimum Ucrit for the handling and commercialization of this species is above of 5,4 body lengths per second.