Freshwater Parr Research Articles

Effect of actinomycin‐D on gill Na+‐K+ ATPase of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Actinomycin‐D reduced gill Na+‐K+ ATPase activity of chinook salmon Oncorhynchus ishawytswha (Walbaum), smolts and saltwater‐adapted juveniles but had no significant effect on the enzyme activity of parr in fresh water. The similarity in response suggests that even though smolts are found in fresh water, their enzyme system is more characteristic of saltwater‐adapted juveniles than freshwater‐dwelling parr. A greater reduction in enzyme activity was found when fish were treated with actinomycin‐D in salt water than in fresh water, suggesting that the enzyme degradation rate wasgreater in salt water than in fresh water.

Plasma growth hormone levels increase during seawater exposure of sexually mature Atlantic salmon parr (Salmo salar L.)

At the time of smoltification in May, smolts and sexually mature male parr were transferred to seawater (25% salinity) and sampled after 6 and 24 hr. Plasma levels of growth hormone (GH) were measured by radioimmunoassay. There was no difference in GH levels between smolts and mature parr in fresh water. GH levels did not change during exposure of smolts to seawater. In the mature male parr, plasma GH levels increased after 24 hr, when the levels were almost five times those of the freshwater controls. In the mature male parr, there was an increase in plasma osmolality, sodium, and magnesium after 24 hr in seawater; magnesium also increased after 6 hr. The levels of potassium and calcium did not change in either immature parr or mature male parr. The increase in plasma GH levels in the mature parr in seawater may be part of a mechanism to increase hypoosmoregulatory ability in fish not ready for seawater entry.

Exposure to seawater stimulates lipid mobilization from depot tissues of juvenile coho (Oncorhynchus kisutch) and chinook (O. tshawytscha) salmon

Tissue lipid content and lipolytic enzyme activity was determined in selected tissues of coho salmon,Oncorhynchus kisutch, at various developmental stages (freshwater parr, freshwater smolt, seawater smolt, and seawater stunt) and in tissues of coho salmon and chinook salmon,O. tshawytscha, exposed to seawater periodically during smoltification. Among developmental groups, total lipid concentration of liver and dark muscle was highest in freshwater (FW) parr. Lipid concentration in both liver and dark muscle was significantly lower in FW smolts, seawater (SW) smolts and SW stunts; no difference was observed among these groups. Alterations in lipid composition were reflected in depot triacylglycerol lipase activity. FW smolts, SW smolts and SW stunts displayed significantly higher lipase activity than FW parr in each of the tissues examined (live, dark muscle and mesenteric fat). Early in smoltification (March, April), exposure to seawater results in enhanced lipid depletion from liver, dark muscle and mesenteric fat, both 30 and 60 days after exposure, compared to FW controls. This depletion was accompanied by increased liver (March and April) dark muscle (March) and mesenteric fat (March) lipase activity. Later in smoltification (May), salinity-induced alterations in lipid metabolism were not observed. These results indicate that exposure to seawater stimulates lipid depletion in juvenile salmon and that the depletion can be explained, in part, by increased depot lipase activity. Furthermore, these data confirm that metabolic dysfunction is associated with stunting.

Inhibition of Salt Water Survival and Na-K-ATPase Elevation in Steelhead Trout (Salmo gairdneri) by Moderate Water Temperatures

Abstract The steelhead trout metamorphosis from a freshwater parr to a sea water-tolerant smolt possessing the migration tendency was evaluated at six different growth temperatures ranging from 6 to 15 C during January through July. The highest temperature where a transformation was indicated was 11.3 C. By April fish reared at 6 C had elevated ATPase levels typical of smolts or migratory animals and showed 92% survival in sea water. Ten and 11.3 C-reared fish showed a short-lived elevation in ATPase in mid-April alone concurrently with 100% sea water survival at that time. Only in 6 C-reared animals did the salt water survival ability continue into May. High ATPase levels likewise were prolonged into May and June only in the 6 C-reared group. The data indicate that metamorphosis (and therefore successful migration) of juvenile steelhead trout is directly controlled by water temperature.