D.T. Nolan

Ambient salinity modulates the response of the tilapia, Oreochromis mossambicus (Peters), to net confinement

Abstract The stress response of the euryhaline tilapia Oreochromis mossambicus adapted to either fresh water (FW) or salt water (Instant Ocean™, 950 mosm; (SW)) was investigated to establish the influences of ambient salinity in this species. The fish were considered to be adapted to the salinities as pre-confinement plasma cortisol and glucose levels were typical for unstressed fish. Two hour net confinement increased plasma cortisol and glucose to a similar extent in both FW and SW. Individual plasma sodium and chloride levels were unaffected by confinement, although plasma Na:Cl ratio increased in FW. Confinement increased intestinal Na + /K + -ATPase activity in FW, but not in SW. In contrast, kidney Na + /K + -ATPase activity increased in SW only. Branchial Na + /K + -ATPase activity decreased with confinement in SW, but not in FW. In SW, confinement reduced the numbers of opercular chloride cells. Increased aging of the branchial chloride cell (CC) population of SW-confined fish was indicated by large numbers of apoptotic CCs in the interlamellar areas. This effect on the CC population was absent in FW-confined fish. Overall, confinement in SW-adapted fish had a more profound impact than confinement in FW-adapted fish. This is likely to have associated energetic consequences in terms of branchial oxygen and ATP consumption. Therefore, results suggest the possibility of different effects of confinement on subsequent growth in FW and SW.

An ecophysiological comparison of wild and hatchery-raised Atlantic salmon (Salmo salar L.) smolts from the Burrishoole system, western Ireland

Abstract Total fish trapping facilities that enable monitoring of all migrating fish have been operating in the Burrishoole river system, west of Ireland, since 1970. Ocean ranching of reared salmon smolts has been used since the early 1960s to supplement grilse returns to the rod fishery and as a research tool for assessing marine survival and exploitation. Wild Burrishoole salmon (Salmo salar) smolts have, on average, a fivefold higher return rate to freshwater than hatchery-reared smolts derived from the same stock. To help explain these differences in return rates, histological and physiological data were collected in 2000 from two groups of hatchery-reared salmon smolts just before release and from wild smolts migrating about the same time. The data show striking differences (size, condition factor (CF), blood cortisol and glucose, gill mucous cells) between both smolt groups. Wild smolt were significantly smaller (mean length: 14.8 and 13.9 cm) and thinner (Mean CF: 0.91 on both dates) than hatchery reared smolt (mean length: 20.3 and 19.1 cm; Mean CF: 1.01 and 1.09). Wild smolt had higher basal cortisol levels in April than in May and did not display “typical” quadratic responses to capture stress, while hatchery-reared smolt did display quadratic cortisol stress responses. Similar differences were observed in serum glucose levels. There was considerable variation in gill and skin histology between fish sampled from the same group, even on the same day, although these were generally present at low levels and were not related to catching order or confinement. Hatchery-reared smolt had significantly higher concentrations of mucous cells in both skin and secondary gill lamellae. This preliminary look at Burrishoole wild and reared salmon smolts indicated striking differences between the two groups which may be linked to subsequent marine survival.

The influence of polychlorinated biphenyl 126 on tilapia (Oreochromis mossambicus) liver

Abstract Tilapia ( Oreochromis mossambicus ) of both sexes were fed a diet containing polychlorinated biphenyl (PCB) 126 (50 μ g kg −1 fish day −1 ) for 5 days to investigate whether a short-term exposure influences liver histology or lipid and glucose metabolism. Semiquantiative electron microscopical analysis confirmed gender-related differences in hepatocyte ultrastructure in sham-treated tilapia as described previously for other fish species. In hepatocytes from males, the amount of glycogen deposits was much larger than in females, as was the number of lipid droplets. Hepatocytes of females had larger amounts of perinuclear rough and smooth endoplasmic reticulum and larger lipid droplets. The treatment led to PCB accumulation in livers of exposed fish to levels previously reported for livers of fish caught from polluted areas. Concurrently, the amount of rough and smooth endoplasmic reticulum and the number of lysosomes increased in the livers of tilapia of both sexes. The cytoplasm became more diffuse and the glycogen space was reduced. In female tilapia lipid droplets increased in number but became smaller in size, while lipid droplets in hepatocytes of males were unaffected. Quantitative light microscopical morphometric analysis of liver sections revealed an increase in cell area after PCB treatment in females only. In males and females a decrease in nuclear area was observed. Because (a) the histological changes observed were moderate and not of an overt pathologic nature, and (b) no changes in basal plasma glucose and free fatty acid levels were observed, it is concluded that the stress-free administration of PCB led to a new equilibrium between mobilisation and tissue uptake of glucose and free fatty acids.

Cortisol influences the host–parasite interaction between the rainbow trout ( Oncorhynchus mykiss ) and the crustacean ectoparasite Argulus japonicus

The host-parasite interaction between the rainbow trout Oncorhynchus mykiss and the fish louse Argulus japonicus was investigated by administering low levels of dietary cortisol before infecting the fish with low numbers of the parasite. After 24 h, the dietary cortisol treatment elevated blood cortisol and glucose levels and stimulated the synthesis of secretory granules in the upper layer of skin cells. Infection with 6 lice per fish caused skin infiltration by lymphocytes, also in areas without parasites. The lymphocyte numbers in the blood at 48 h post-parasite infection were reduced. Other changes, typical for exposure to many stressors and mediated by cortisol, were also found in the epidermis of parasitized fish, although neither plasma cortisol nor glucose levels were noticeably affected. Glucocorticoid receptors were localized immunohistochemically and found in the upper epidermal layer of pavement and filament cells, and in the leucocytes migrating in these layers. Cortisol-fed fish had reduced numbers of parasites and the changes in the host skin are likely involved in this reduction. Thus a mild cortisol stress response might be adaptive in rejecting these parasites. Further, the data suggest that this effect of cortisol is mediated by the glucocorticoid receptor in the skin epidermis, as these are located directly at the site of parasite attachment and feeding in the upper skin cells that produce more secretory granules in response to cortisol feeding.

Characterization of primary culture of rainbow trout (Oncorhynchus mykiss) skin explants: Growth, cell composition, proliferation, and apoptosis

SummaryA trout (Oncorhynchus mykiss) epidermal skin primary explant system was evaluated over 8 d by light and electron microscopy. Three distinct regions of the explant outgrowth were identified on the basis of cell composition. The area immediately adjacent to the founder tissue contained mainly small migrating cells and mucous cells. Of the former, about 20% were mitotic and 6% apoptotic. The middle area was characterized by differentiated pavement cells and mucous cells, with fewer small migrating cells. Proliferation was approximately 30% and apoptosis 5%. Over time, total cell numbers halved as more pavement cells differentiated. The growing front contained many mucous and small migrating cells initially, with few pavement cells. About 50% of the cells were in the proliferative phase, and 5% were apoptotic. Later, there were fewer migrating and mucous cells, with a higher number of pavement cells. About 9% of the cells were apoptotic, and 70% of the cells were proliferating. As in vivo, pavement cells had apical microridges, although they were vacuolated and contained phagocytosed apoptotic bodies. The data and observations are based on the numbers of cell cultures prepared from separate trout giving the sample size n=7. As this culture system is reproducible and closely approximates the epidermis of trout, it is a powerful tool to study the effects of pollutants, parasites, and endocrine factors on fish skin, eliminating whole-animal factors and reducing the number of experimental animals required.