Responses of a non-migratory stock of brown trout, Salmo trutta, to ovine growth hormone treatment and seawater exposure

The ability of ovine growth hormone (oGH) to enhance the hypo-osmoregulatory performance of a non-migratory stock of the brown trout (Salmo trutta) was investigated. Three groups of juvenile fish were intraperitoneally implanted either with a cholesterol pellet (sham) or with a cholesterol pellet containing 250 μg oGH (treated); control fish did not receive any implant. While still in fresh water, the gill Na+⁄K+-ATPase activity of the oGH-treated group was four times higher than that of sham and control groups 2 weeks after implantation. Transfer to sea water (SW) resulted in marked increases in plasma electrolyte levels of the sham and control groups, whereas the oGH-treated group showed only minor perturbations in plasma electrolyte concentrations. Subsequent regulation of plasma electrolyte parameters to lower levels was slower or less effective in the non-treated groups than in the oGH-treated group. In the non-treated groups, SW exposure brought about significant increases in gill Na+⁄K+-ATPase activity but only after a time lag of 7 days. An additional significant increase in gill Na+⁄K+-ATPase activity was also observed in the oGH group 7 days after SW exposure. By the end of the experiment, oGH-treated fish were significantly larger than non-treated ones. The data indicate that after oGH administration, juvenile non-smoltifying brown trout respond to SW exposure in the same manner as a fully smolted salmonid

Toxicidade aguda do nitrito em larvas do peixe-rei marinho Odontesthes argentinensis (Teleostei, Atherinopsidae) Acute toxicity of nitrite on larvae of the marine pejerrey Odontesthes argentinensis (Teleostei, Atherinopsidae)

Este trabalho visou a determinar o efeito tóxico do nitrito sobre larvas do peixe-rei marinho Odontesthes argentinensis através de testes agudos com 96h de duração. As larvas utilizadas neste experimento foram cultivadas no Laboratório de Maricultura da FURG (Rio Grande - RS). Foi utilizada água do mar filtrada na salinidade 35‰, na temperatura de 23&deg;C, com fotoperíodo de 14 horas de luz e aeração constante. Diariamente, as larvas mortas foram retiradas e, em seguida, 100% do meio experimental foi renovado. Não foi fornecido alimento durante a exposição ao nitrito. As larvas foram expostas a cinco concentrações de nitrito: 50, 150, 250, 350 e 450mg L-1 N-NO2-, mais um controle onde o nitrito não foi adicionado. A CL50-96h (concentração letal para 50% dos organismos após 96 horas) e seu intervalo de confiança (95%) foram de 199,3 (142,0-279,6)mg L-1 N-NO2-. Os resultados deste trabalho sugerem que, assim como outras espécies de peixes marinhos, o O. argentinensis é uma espécie tolerante a altas concentrações de nitrito e é pouco provável que este último seja um problema para o cultivo intensivo desta espécie.<br>This work evaluated the toxicity of nitrite on larvae of the marine pejerrey Odontesthes argentinensis through acute exposure during 96h. Larvae used in this experiment were cultivated in the Laboratory of Mariculture of the University of Rio Grande. During the tests temperature was 23&deg;C, salinity 35‰, and 14 hours of light were provided. Every day dead larvae were removed and the experimental media were completely renewed. Larvae were deprived of food during the test. Concentrations for the acute tests were 50, 150, 250, 350 and 450mg L-1 N-NO2-, plus a control with no nitrite added. Lethal concentration for 50% of the organisms (LC50-96h), and its confidence interval, was 199.3 (142.0-279.6)mg L-1 N-NO2-. The results of the acute tests suggest that, as other species of marine fish larvae, O. argentinensis is tolerant to high concentrations of nitrite, and it is unlikely that it would be a problem for the intensive culture of this species