• Fisheries and Aquatic Sciences
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• v.13 no.4
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• pp.343-349
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• 2010

The effects of osmotic stress on the non-specific immune response of Nile tilapia, Oreochromis niloticus, were investigated. Osmoregulatory mechanism of tilapia has been studied, but less information is available about innate immune response of O. niloticus faced with hyperosmolality. Acute osmotic stress was elicited by transferring tilapia from freshwater (FW) to 24 psu seawater (SW). Non-specific immune parameters including lysozyme activities of plasma and head kidney (HK), alternative complement pathway (ACP) activity in plasma, phagocytic capacities of spleen and HK immune cells, and respiratory burst activity of immune cells in both HK and spleen were analyzed. Lysozyme activities were increased at 1 h and 30 h after transfer to SW, but decreased at 10 h after SW transfer. Conversely, ACP activity increased 10 h after SW transfer. Phagocytic capacity increased slightly at 1 h and 5 h after SW transfer, and respiratory burst activity showed an increase in superoxide release at 10 h after SW transfer. Taken together, these results indicate that the exposure of tilapia to hyperosmotic conditions has immunostimulatory effects on cellular and humoral immune reactions.

• Development and Reproduction
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• v.24 no.3
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• pp.215-224
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• 2020

Seawater adaptability of steelhead trout increases along with the increase in the size of the fish, independent of parr-smolt transformation. Three 96 h seawater challenge tests were conducted to determine the size at which seawater adaptability of steelhead trout develops. Plasma Na⁺ and Cl^- levels, moisture content, gill Na⁺/K⁺ ATPase activity, and mortality during the 96 h after direct transfer to seawater (32 ppt) were determined. Plasma Na⁺ and Cl^- levels in 50 g fish continuously increased during the 96 h after the transfer to seawater (p<0.05), but the levels in 100 and 150 g fish leveled off after 24 h (p<0.05). Both 100 and 150 g size steelhead trout maintained muscle moisture content (%) better than 50 g size fish (p<0.05). Gill Na⁺/K⁺ ATPase activity in the 100 g size group increased in a time-dependent manner after transfer to seawater (p<0.05), whereas activity in the 50 and 150 g sizes did not increase (p>0.05), for which a possible explanation was discussed. A mere 2.6% mortality in both the 50 and 150 g size groups was observed. In conclusion, the current results indicate that 50 g size steelhead trout did not show development of a high level of hypoosmoregulatory capacity, whereas fish in the 100 and 150 g size groups showed a high level in our experimental conditions. Therefore, the steelhead trout larger than a 100 g size is recommended for transfer to seawater culture.

• Korean Journal of Ichthyology
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• v.22 no.1
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• pp.9-16
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• 2010

Osmoregulatory capabilities of a euryhaline medaka, Oryzias dancena (Beloniformes; Teleostei), was examined with a particular emphasis on adult and larval viability during direct salinity changes. O. dancena adults were highly capable for hyper-osmoregulation as well as hypo-osmoregulation, as evidenced by no adverse effect on their viability during the direct transfer either from complete freshwater ($0^{\circ}/_{\circ\circ}$) to $40^{\circ}/_{\circ\circ}$ salinity, or from $70^{\circ}/_{\circ\circ}$ to $0^{\circ}/_{\circ\circ}$. Furthermore, the phased increase of external salinity with acclimation periods allowed them to survive at a salinity as high as $75^{\circ}/_{\circ\circ}$. However, tolerant capability to acute salinity increase in early larval stage was much less than in adult stage, based on the finding that the tolerance range of salinity increase was only $15^{\circ}/_{\circ\circ}$ from freshwater, indicating that the hyper-osmoregulation system might not be fully developed in the early larval stage. On the contrary, the hypoosmoregulation system could be more solidified in O. dancena larvae, as evidenced by their good survival even after direct transfer from $45^{\circ}/_{\circ\circ}$ to $0^{\circ}/_{\circ\circ}$. Knowledge achieved in this study could form the basis for a wide scope of researches including ecotoxicogenomics and geneexpression assay using this model species.

• Journal of Aquaculture
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• v.19 no.3
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• pp.149-156
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• 2006

Stress responses, osmoregulation and growth of black porgy reared in freshwater or seawater were investigated by supplying the feed (10 mg/kg feed) treated with the $T_3$ (3,5,3'-triiodo-L-thyronine) for 90 days. Plasma $T_3$ in black porgy reared for 60 days in freshwater with (FT) or without (FN) $T_3$, treatment was lower than that in black porgy reared in seawater with (ST) or without (SN) $T_3$ treatment. The concentration of $T_3$ in FT was significantly more than that in FN. Plasma cortisol in FT, at the same day, was 4 times higher than that in FN, whereas the differences of the hormone between ST and SN was not significant. Although the levels of plasma glucose in FN and FT tended to be lower than that in ST and SN, no differences were found between fish reared in freshwater and seawater after $T_3$ treatment. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of black porgy reared in seawater showed no difference throughout the experimental period. However, at the beginning stages of the experiment, the plasma levels of these enzymes in FN and FT were higher than in SN and ST. Recovering of AST level to the level of SN or FT was laster in FT than in FN. However, no effects of the exogenous $T_3$ treatment on osmoregulatory capacity and growth of black porgy reared in freshwater or seawater were observed in this study.