Geology topics
J.E. Halver
Publications and source records attributed to J.E. Halver.
Chemical and histological studies of wild and hatchery salmon in fresh water
In a study of coho salmon ( Oncorhynchus kisutch ), the gross chemical and histological changes occurring over a 14-month period spent in fresh water were determined. The determinations were made at 3-month intervals on: 1) hatchery-reared fish, 2) fish hatchery-reared for 3, 6, 9, and 12 months and then planted in a controlled stream for the remainder of the period; and 3) an indigenous group of wild fish in this stream. Wild fish showed high incidence of tissue damage from spinose hairs of the moth larva, Halisidota argentata. Hatchery fish were similarly affected with the severity and incidence of lesions varying directly with the time of exposure of the larvae in the wild environment. Both groups of fish were heavily parasitized by sporozoan organisms in the kidney and spinal cord. Kidney disease appeared in both wild and planted hatchery fish. The gross chemical composition of hatchery fish transformed rapidly after planting to that of the wild fish. Although the initial rate of fat loss is essentially constant for all hatchery groups after planting, fish that were hatchery reared for 9 to 12 months did not complete the transformation to the wild-type body composition by the time of downstream migration at 14 months.
The nutrition of salmonid fishes. I. Chemical and histological studies of wild and domestic fish
Salmonids reared under artificial conditions show marked consistent differences in body composition in comparison with wild salmonids. Protein and mineral levels are lower and lipid values are higher in hatchery fish than in wild fish. As the period of artificial rearing is increased, these differences become more extreme. In hatchery fish, there is generally more microscopically visible fat in the liver and viscera than in these organs in wild fish although extremes are seen in both groups. In young hatchery fish and in wild fish, there is no correlation between fat deposition in the liver and in the pancreas, but in older hatchery fish, both of these organs are fatty and there is a simultaneous increase in total body lipid. In wild fish, ceroid deposition is greater, suggesting that the fatty acids are more highly unsaturated. There is little difference in disease incidence between the two groups, but parasitism is more pronounced in wild fish. The significant variables between wild and artificially produced fish appear to be limited to diet and environment. From the factors discussed above, diet alone is probably the most important single factor in producing the changes observed in body composition.
The nutrition of salmonid fishes. II. Studies on production diets
In 69 production diets fed to hatchery salmonids, there was a wide variation in the ingredients of the diets and in their content of protein, fat, carbohydrate and ash. There was a close correlation between the body composition of hatchery-raised fish and the composition of the diets fed. The data indicated, however, that differences in hatchery management, such as level of feeding, were also important contributing factors in producing the observed body composition of hatchery fish. Wild fish had a markedly different body composition characterized by a much lower level of fat and relatively higher protein and mineral content The effect on survival of differences in body composition between wild and hatchery fish is discussed. There is a clearly defined need for additional research on the nutritional requirements of salmonids, the relationship between body composition and ability to survive, and for quality control in hatchery nutrition.