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Carotenoid utilization in rainbow trout (Oncorhynchus mykiss Walbaum) and Atlantic salmon (Salmo salar L.) has been investigated with respect to tissue distribution of carotenoids and the role of the liver on the bioavailability of the lipid soluble carotenoids, astaxanthin and canthaxanthin. Species-specific and tissue-specific accumulations were noted for astaxanthin and canthaxanthin in the rainbow trout and Atlantic salmon, possibly indicating fundamental differences in their utilization in these species. The liver and the kidney were revealed to be the major tissues involved in carotenoid metabolism in both rainbow trout and Atlantic salmon. Apparent digestibilities (-96% and -30% for rainbow trout and Atlantic salmon, respectively) and flesh carotenoid retentions (-12% and -5.4% for rainbow trout and Atlantic salmon, respectively) differed significantly between species, suggesting that rainbow trout are more efficient depositors of carotenoids within the flesh. Isolated rainbow trout liver perfusion experiments revealed small differences in the uptake of astaxanthin and canthaxanthin. Uptake of astaxanthin in both synthetically-derived and serum-derived models showed saturable uptake mechanism that occurred earlier than for canthaxanthin. These results can potentially offer an explanation for the better utilization of astaxanthin in rainbow trout, where the liver reduces the bioavailability of canthaxanthin through continued uptake. Results show a low hepatic extraction ratio (0.03-0.07), in line with published post-prandial elimination rates. Neither astaxanthin nor canthaxanthin significantly induced hepatic or renal xenobiotic-metabolizing enzymes in the rainbow trout, contrary to published reports in rats and mice. This may imply fundamental species-specific differences in the metabolic pathways for these carotenoids. Histochemical investigations revealed that both carotenoids significantly impacted liver structure, resulting in higher levels of total lipids and mucopolysaccharides. This is thought to be due to their antioxidant functions and their provitamin A activity. Carotenoid-treated fish also had higher levels of glycogen phosphorylase in liver sections, providing the first evidence in fish for the possibility of glucuronidation of their metabolites. The present investigations demonstrate the liver to be a major organ in carotenoid metabolism, and consequently affects carotenoid distribution and availability. In addition, carotenoid supplementation significantly affects liver structure and may potentially enhance its function. Furthermore, these investigations have provided new avenues of investigation into the use of isolated organ perfusions for biochemical nutrition research, and expanded the knowledge of liver physiology and biochemistry.

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The first part of this study investigated the effects of varying temperature regimes within the range of 8-22°C on the development and survival of Atlantic salmon (Salmo salar L.) eggs and alevins. The temperature tolerance of eggs was lower than that of alevins: egg mortality increased above 11°C and no eggs survived to eyeing or to hatching at 16 and 14°C, respectively; alevin mortality increased above 16°C and no alevins survived at 22°C. Optimal survivals of eggs and alevins occurred at 8-11°C and 10-14°C, respectively. Subsequent survival at later stages of development was largely determined by survival at earlier stages. Developmental abnormalities among eggs (pin-eyed eggs) and alevins (abnormal hatching and yolk-sac oedema) appeared to be temperature-dependent. Development time in days from fertilisation to eyeing, hatching and maximum alevin wet weight (MAWW) varied inversely with temperature. The sum of degree-days from fertilisation to eyeing and to MAWW was similar at all temperatures, but declined with increasing temperature from eyeing to hatching. The hatching period was similar for all temperatures except 8°C where it was significantly longer. Although alevin size at hatching was not temperature-dependent within the range of 8-12°C, alevin size at MAWW decreased progressively with increasing temperature (10-20°C) during the alevin stage. Fry size at first feeding did not affect their subsequent growth rate or survival. Advanced fry which were fed earliest grew at similar rates to those produced at lower temperatures and attained the greatest weight. Biomass gain was more dependent upon survival than upon mean fish weight. The second part of this study investigated the effects of timing of first feeding on fry growth and survival. Alevins fed prior to final yolk resorption were larger and had lower mortalities than those fed after MAWW. Although the "window" of first feeding opportunity lasted several weeks, delaying feeding beyond MAWW reduced absolute growth. A 5-week delay led to mortalities approaching 60%. However, first feeding can be delayed beyond MAWW for 1-2 weeks at 10°C without adversely affecting subsequent survival or growth rate.

Mémoire (M. Sc.)-- Université du Québec à Chicoutimi, 1985. / Bibliogr.: f. 99-102. Document électronique également accessible en format PDF. CaQCU

Thesis (Ph.D. )--Memorial University of Newfoundland, 1997. / Bibliography: leaves 118-145.

Thesis (Ph.D.) in Zoology--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 95-108).

Thesis (Ph. D.)--University of Rhode Island, 2006. / Includes bibliographical references (leaves 138-154).

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