Walton W. Dickhoff

The role of growth in endocrine regulation of salmon smoltification

Keywords: growth, salmon, smoltification, insulin, insulin-like growth factor I (IGF-I), growthhormone, thyroxine, photoperiod, temperature, nutritioncreases hepatic IGF-I mRNA (Cao et al. 1989;Sakamoto and Hirano 1993; Duan et al. 1994) andelevates blood IGF-I levels (Moriyama et al.1994). The majority of IGF-I in salmonid blood isprobably bound to specific binding proteins(IGFBPs), some of which are influenced by GH,insulin and nutrition (Kelley et al. 1992; Siharathand Bern 1993). The IGFBPs in blood and in tis-sues surrounding target cells undoubtedly play asignificant role in modifying the action of IGF-Iin fish, as they do in mammals, although this islargely unexplored in the context of salmon smol-tification. IGF-I inhibits GH release by negativefeedback, as shown

Assessment of High Rates of Precocious Male Maturation in a Spring Chinook Salmon Supplementation Hatchery Program

Abstract The Yakima River Spring Chinook Salmon Supplementation Project in Washington State is one of the most ambitious efforts to enhance a natural salmon population currently under way in the United States. Over the past 5 years we have conducted research to characterize the developmental physiology of natural and hatchery-reared wild progeny spring Chinook salmon Oncorhynchus tshawytscha in the Yakima River basin. Fish were sampled at the main hatchery in Cle Elum, at remote acclimation sites, and, during smolt migration, at downstream dams. Throughout these studies, we characterized the maturational state of all fish using combinations of visual and histological analyses of testes, computation of gonadosomatic indices, and measurement of plasma 11-ketotestosterone (11-KT). We established that a plasma 11-KT threshold of 0.8 ng/mL can be used to designate male fish as either immature or precociously maturing approximately 8 months prior to final maturation (1–2 months prior to release as “smolts”). Ou...

Physiological Status of Naturally Reared Juvenile Spring Chinook Salmon in the Yakima River: Seasonal Dynamics and Changes Associated with Smolting

Abstract Two year-classes of juvenile spring chinook salmon Oncorhynchus tshawytscha from the Yakima River, Washington, were sampled from July (3–4 months postemergence) through May (yearling smolt out-migration). Physiological characters measured included liver glycogen, body lipid, gill Na+-K+ ATPase, plasma thyroxine (T4), and plasma insulin-like growth factor-I (IGF-I). Distinct physiological changes were found that corresponded to season. Summer and fall were characterized by relatively high body lipid and condition factor. Winter was characterized by decreases in body lipid, condition factor, and plasma hormones. An increase in condition factor and body lipid was found in February and March. Finally, April and May were characterized by dramatic changes characteristic of smolting, including increased gill Na+-K+ ATPase activity, plasma T4, and IGF-I and decreased condition factor, body lipid, and liver glycogen. These results create a physiological template for juvenile spring chinook salmon in the d...

Growth, smoltification, and smolt-to-adult return of spring chinook salmon from hatcheries on the Deschutes River, Oregon

Abstract The relationship between smoltification and smolt-to-adult return (SAR) of spring chinook salmon Oncorhynchus tshawytscha from the Deschutes River, Oregon, was examined for four release groups in each of three successive years. Fish were reared, marked with coded wire tags, and released from Round Butte Hatchery, Pelton Ladder rearing facility, and Warm Springs National Fish Hatchery. Smolt releases occurred in nearly the same place at similar times, allowing a direct comparison of SAR to several characters representing smolt quality. Return rates varied significantly among facilities, varying over an order of magnitude each year. The highest average SAR was from Pelton Ladder, the lowest was from Warm Springs. Each of the characters used as metrics of smoltification—fish size, spring growth rate (February–April), condition factor, plasma hormone concentration (thyroxine, cortisol, and insulin-like growth factor-I [IGF-I]), stress challenge, gill Na+, K+-ATPase activity, and liver glycogen concen...

Effects of injected and dietary arginine on plasma insulin levels and growth of Pacific salmon and rainbow trout

1. n1. Amino acids (arginine, alanine and lysine) injected intraperitoneally 6.6 μmol/g body weight elevate, while histidine decreases plasma circulating levels of insulin in coho salmon (Oncorhynchus kisutch). n n2. n2. Insulinotropic action of arginine (0.03–6.6 μmol/g body weight) can be observed at 0.5–5.0 hr after injection. The effect of arginine is dependent on the season being more prolonged in winter when water temperature is low. n n3. n3. Insulinotropic action of arginine seems to be direct rather than through stimulation of glucagon or glucagon-like peptide secretion. n n4. n4. Feeding coho salmon, Chinook salmon (O. tshawytscha) and rainbow trout (O. mykiss) diets supplemented with arginine caused elevation of plasma insulin levels. Arginine supplemented diets (20–30 g/kg dry diet over the content of regular diet) had a short-lasting stimulatory effect on fish growth, an effect which could be detected only in fingerlings.

Relation of Fish Size and Growth Rate to Migration of Spring Chinook Salmon Smolts

Abstract We examined the relation of size and growth rate to downstream migration in yearling spring chinook salmon Oncorhynchus tshawytscha. A group of juvenile chinook salmon was graded by size into small and large categories; half the fish in each category were reared at an elevated temperature beginning in mid-February, resulting in four distinct treatment groups: large–warm, large–cool, small–warm, and small–cool. Fish from warmwater treatment groups displayed significantly higher growth rates through the spring than coolwater groups. Fish were released into a natural creek on two dates (25 March, release 1 and 12 April, release 2), and downstream movement was monitored. For each release, fish that migrated past a weir within the first 5 d postrelease had significantly higher spring growth rates than fish that did not migrate within that period. A similar comparison of release length to migration demonstrated significant differences only in release 2. Also for release 2, fish from the large–warm and ...

The effect of insulin on amino acid metabolism and glycogen content in isolated liver cells of juvenile coho salmon, Oncorhynchus kisutch ☆

Amino acid transport and [14C]leucine incorporation into liver proteins as well as the secretion of proteins into incubation medium were studied in liver cells isolated from coho salmon (Oncorhynchus kisutch) parr. Pink salmon (Oncorhynchus gorbuscha) or mammalian (bovine) insulin caused a significant increase in TCA-precipitable radioactivity from both cells and incubation medium. The effects appeared at insulin concentration of 10(-8) M with a maximal response at 5 X 10(-8) M. The radioactivity of the TCA-soluble fraction was not changed by insulin. Insulin increased the amount of the non-metabolized amino acid [14C]cycloleucine, in the TCA-soluble fraction of hepatocytes. The glycogen content of hepatocytes was increased in the presence of insulin at 10(-9) M but was not changed from the control value in the presence of insulin at 10(-8) M.

Life history plasticity in chinook salmon: relation of size and growth rate to autumnal smolting

Abstract An experiment was conducted to assess the relative influence of body size and growth rate on autumnal smolting of under-yearling spring chinook salmon. Fish were sorted into large (>85 mm) or small ( + –K + –ATPase, plasma T 4 and IGF-I were obtained at 2-week intervals. On seven occasions throughout October and November, 10 fish from each treatment group were PIT tagged and movement patterns were assessed. Autumnal smolting clearly occurred in all treatment groups, indicated by elevated gill Na + –K + –ATPase activities, attainment of a silvery skin coloration, and an active swimming behavior pattern. However, fish from the Large-HiFeed treatment clearly differed in a number of respects from fish from the Small-LoFeed treatment from August through September: condition factor was higher, skin was more silvery, plasma T 4 and IGF-I levels were higher, and gill Na + –K + –ATPase activities were higher. In addition, fish from the Large-HiFeed group showed greater levels of activity than fish from the Small-LoFeed group on most occasions, in October and November. These data extend knowledge of the phenomenon of autumnal smolting in chinook salmon. Further, they demonstrate that differences in growth through the summer–autumn period has a significant effect on both physiological and behavioral expression of smolting.

Metabolic hormones regulate basal and growth hormone-dependent igf2 mRNA level in primary cultured coho salmon hepatocytes: effects of insulin, glucagon, dexamethasone, and triiodothyronine

Igf1 and Igf2 stimulate growth and development of vertebrates. Circulating Igfs are produced by the liver. In mammals, Igf1 mediates the postnatal growth-promoting effects of growth hormone (Gh), whereas Igf2 stimulates fetal and placental growth. Hepatic Igf2 production is not regulated by Gh in mammals. Little is known about the regulation of hepatic Igf2 production in nonmammalian vertebrates. We examined the regulation of igf2 mRNA level by metabolic hormones in primary cultured coho salmon hepatocytes. Gh, insulin, the glucocorticoid agonist dexamethasone (Dex), and glucagon increased igf2 mRNA levels, whereas triiodothyronine (T(3)) decreased igf2 mRNA levels. Gh stimulated igf2 mRNA at physiological concentrations (0.25x10(-9) M and above). Insulin strongly enhanced Gh stimulation of igf2 at low physiological concentrations (10(-11) M and above), and increased basal igf2 (10(-8) M and above). Dex stimulated basal igf2 at concentrations comparable to those of stressed circulating cortisol (10(-8) M and above). Glucagon stimulated basal and Gh-stimulated igf2 at supraphysiological concentrations (10(-7) M and above), whereas T(3) suppressed basal and Gh-stimulated igf2 at the single concentration tested (10(-7) M). These results show that igf2 mRNA level is highly regulated in salmon hepatocytes, suggesting that liver-derived Igf2 plays a significant role in salmon growth physiology. The synergistic regulation of igf2 by insulin and Gh in salmon hepatocytes is similar to the regulation of hepatic Igf1 production in mammals.

The effects of estradiol and triiodothyronine on protein synthesis by hepatocytes of juvenile coho salmon (Oncorhynchus kisutch).

A method was developed for studying the in vitro metabolism of radiolabeled amino acids by dispersed salmon hepatocytes. Radioactivity accumulated in trichloroacetic acid (TCA)-precipitable and -soluble fractions of cells and in TCA-precipitable fractions of incubation medium was measured. Estradiol (E2) or triiodothyronine (T3) stimulated the amount of radioactivity in the TCA-precipitable fraction of cells in a dose-dependent manner. T3 caused an increase in TCA-soluble radioactivity of cells that were incubated with [14C]serine, [14C]glycine or the nonmetabolizable amino acid [14C]cycloleucine. E2 had either no effect or caused a decrease in TCA-soluble radioactivity in cells that were incubated with [14C]serine or [14C]glycine. E2 increased TCA-soluble radioactivity in cells that were incubated with [14C]cycloleucine. E2 but not T3 caused an increase in TCA-precipitable radioactivity in the medium from incubation of hepatocytes with metabolizable radioactive amino acids. These results suggest that protein metabolism by salmon hepatocytes is stimulated by both E2 and T3 with differing kinetic patterns.