Development of osmotic and ionic regulation in two races of chinook salmon Oncorhynchus tshawytscha

Experimental production of gastric dilation and its association with osmoregulatory stress and biogenic amines in chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Chinook salmon smolt in fresh water fed a commercial diet known to produce minimal gastric dilation and air sacculitis (GDAS) were randomly assigned to four experimental tanks with flow-through sea water. All four groups were acclimatized to sea water for 3 weeks and fed a diet of minced fresh seafood. After 3 weeks the groups were fed either; seafood as before, a different commercial pelleted diet associated with the development of GDAS on farms, or either diet supplemented with 500 mg L(-1) putrescine, 300 mg L(-1) cadaverine and 250 mg L(-1) tyramine. Gastric dilation was produced in fish fed the commercial diet for 1 month but not by feeding a diet of minced seafood. The addition of putrescine, cadaverine and tyramine to either diet had no significant effect on the development of gastric dilation. Fish fed the commercial diet had significantly (P < 0.0001) wider weight-adjusted stomach widths, less prominent longitudinal stomach folds (P < 0.0001) and lower (P < 0.0001) stomach-width ratios than fish fed the fresh seafood diet. There was no significant difference in serum osmolality or sodium concentration between fish from groups with or without gastric dilation or fed biogenic amines.

Insulin-like growth factor-I and environmental modulation of growth during smoltification of spring chinook salmon (Oncorhynchus tshawystscha)

The relations among rearing environment, fish size, insulin-like growth factor-I, and smoltification were examined in yearling spring chinook salmon (Oncorhynchus tshawytscha). Juvenile chinook salmon were size-graded into small and large categories. Half of the fish in each group were reared at an increased temperature and feeding rate beginning in mid-February, resulting in four distinct treatment groups: large warm-water (LW), large cool-water (LC), small warm-water (SW), and small cool-water (SC). Increased temperature and feeding rate resulted in overall higher growth rates for the LW and SW groups. Temporal increases in insulin-like growth factor-I (IGF-I) were found in all groups through the spring. Plasma IGF-I levels were significantly higher in warm-water groups than in cool-water groups from late March through May. Size itself appeared to have little relation to plasma IGF-I levels. Simple regression showed a significant relation between plasma IGF-I and growth (P < 0. 001, R2 = 0.50). No differences were found between treatment groups in other physiological parameters assessed (plasma thyroxine, gill Na+-K+-ATPase, liver glycogen, body lipid).

Survival of salmonids in seawater and the time-frame of growth hormone action

In salmonids, growth hormone (GH) effectively promotes adaptation of freshwater (FW) fish to seawater (SW), but it has been unclear whether GH has osmoregulatory actions apart from those consequent to an increase in body size. Our objectives were first, to examine the minimum time and dose required for GH to enhance SW adaptation; and second, to optimize the conditions for the acute GH response in developing a convenient GH bioassay based on its plasma ion lowering effect. Trout showed markedly improved SW survival when transferred from fresh water 6, 24, or 48h after a single chum salmon GH injection (0.25 μg/g). Preadapting trout to 1/3 SW enhanced the plasma ion lowering effect of ovine GH (oGH) injected 48h before transfer of the fish to 80% SW. Endogenous plasma GH levels were elevated in control trout switched from low salinities to 80% SW but were depressed in oGH-injected fish after transfer. Under optimal test conditions (1/3 SW preadaptation, 48h pre-transfer injection, and 100% SW final challenge), the reduction in plasma Na(+), Ca(++), and Mg(++) levels of oGH-injected fish was dose-dependent. The oGH doses giving minimum and maximum responses were 50 and 200 ng/g, respectively. In short, GH exerts acute osmoregulatory actions that promote SW adaptation in the absence of changes in body size. Compared with growth GH bioassays, the osmoregulatory assay is superior in economy of time, animal costs, and hormone quantity required and potentially in specificity.

Seasonal changes in pineal melatonin content and hydroxyindole-O-methyltransferase activity in juvenile chinook salmon, Oncorhynchus tshawytscha

Juvenile fall and spring chinook salmon were examined for seasonal changes in pineal hydroxyindole-O-methyltransferase (HIOMT) activity. Numerous small peaks in pineal HIOMT specific activity were found in fall chinook salmon and HIOMT activity per pineal gland increased linearly with age and/or size. In spring chinook salmon, cyclic changes in pineal HIOMT specific activity occurred in midsummer and midwinter, independent of the photoperiod under which the fish were reared. HIOMT activity per pineal gland showed a peak in midwinter. Activity increased with age and/or size of the fish during the following spring. Melatonin content of the pineal gland of spring chinook salmon did not change seasonally in fish reared under a normal photoperiod. Fish reared under constant illumination had about 50% higher pineal melatonin content than those under a normal photoperiod until November. At that time, pineal melatonin content decreased to the same level as that of fish reared under a normal photoperiod.

Smolt Transformation: Evolution, Behavior, and Physiology

Literature concerned with the appearance of smolts (silvery color, streamlined body form), their physiology (salinity relationships, endocrinology), and their behavior (territorial and schooling) is discussed in relation to key steps that may have been taken in the evolution of the parr–smolt transformation and seagoing behavior. In this discussion, it is assumed that Salmonidae evolved in fresh water, that the genus Oncorhynchus originated in a large area of brackish water such as the Sea of Japan, and that schooling oncorhynchids (for example O. gorbuscha and O. keta) are the most specialized of the seagoing salmonids while species of char (Salvelinus) and trout (Salmo) are more primitive.