Search

Low levels of stresses cause eustress while high stressful situations result in distress. Female rainbow trout (Oncorhynchus mykiss) was reared under crowded conditions to mimic the stressful environment of intensive fishery production. Trout was stocked for 300 days with initial densities of 4.6 ± 0.02 (final: 31.1 ± 0.62), 6.6 ± 0.03 (final: 40.6 ± 0.77), and 8.6 ± 0.04 (final: 49.3 ± 1.09) kg/m3 as SD1, SD2 and SD3. We assessed molecular, cellular and organismal parameters to understand the flexibility of neuro-endocrine-immune network during stress. Trout with higher initial density (SD3) displayed the slightly activated hypothalamus-pituitary-interrenal (HPI) axis with positively increased antioxidant enzyme activities and anti-inflammatory cytokine transcriptions on day 60 or 120. These results indicated that low level of stress was capable of exerting eustress by activating neuro-endocrine-immune network with beneficial adaptation. Transition from eustress to distress was induced by the increased intensity and duration of crowding stress on day 240 and 300. The prolonged activation of HPI axis resulted in suppressed growth hormone-insulin-like growth factor (GH-IGF) axis, up-regulated cytokine transcriptions and severe reactive oxygen species stress. Stress means reset of neuro-endocrine-immune network with energy expenditure and redistribution. Digestive ability of trout with distress was also inhibited on day 240 and 300, indicating a decreased total energy supplement and energy distribution for functions are not necessary for surviving such as growth and reproduction. Consequently, we observed the dyshomeostasis of energy balance and neuro-endocrine-immune network of trout during long-term crowding conditions. Image 1 • Low levels of crowding stress provided eustress with positive HPI activation. • Eustress stimulate adaptive mechanisms in endocrine and immune network. • Long-term crowded conditions cause distress with negatively prolonged HPI activation. • Distress caused maladaptive mechanisms in endocrine and immune network. [ABSTRACT FROM AUTHOR]

To study the expression of four estrogen receptor genes ( erα1, erα2, erβ1, erβ2 ) of female rainbow trout ( Oncorhynchus mykiss ) during first ovarian development, trouts were sampled from different ovarian stages. Serum E 2 (estradiol) was measured by ELISA and estrogen receptors mRNA expression were examined by qRT-PCR. Our results showed a close association between increased erα1 and vitellogenin mRNA expression during ovarian maturation and increased erα2 mRNA expression in mature ovarian stages. Correlation analysis revealed that a negative relationship between serum E 2 and ovarian erβ1 (or hepatic erβ2 ), but ovarian erβ2 mRNA expression was relatively unchanged during first ovarian development. Trout were also reared in different densities as stocking density 1, 2 and 3 (SD1, 4.6–31.1 kg/m 3 ; SD2, 6.6–40.6 kg/m 3 ; SD3, 8.6–49.3 kg/m 3 ) to elucidate effects of high density on estrogen receptor expression. Histology observation showed ovarian development of trout in higher densities were retard with a relatively early stage and fewer vitellogenin accumulation. Trout in high densities showed significantly decreased serum E 2 , erα mRNA expression and increasing trends of erβ mRNA expression. A noticeable increase of ovarian erβ2 mRNA expression was seen in trout when density is approaching to 50 kg/m 3 . In conclusion, we may hypothesize that increased erβ mRNA expression triggered by high density result in decreased erα mRNA expression and vitellogenesis. As a result, ovarian development in higher densities was retard. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the hypothalamus-pituitary-gonad (HPG) axis of female rainbow trout ( Oncorhynchus mykiss ) during early ovarian development and under high rearing density. Trouts were sampled from 240 (ovarian stage II) to 540 (ovarian stage IV) days following hatching (DFH) as control group (Ctrl, 4.6–31.1 kg/m 3 ) to determine HPG axis during early ovarian development. Trouts from the same batch of fertilized eggs were reared in two higher densities during 240–540 DFH as stocking density 1 and 2 (SD1, 6.6–40.6 kg/m 3 ; SD2, 8.6–49.3 kg/m 3 ) to elucidate effects of high density on reproductive parameters. Dopamine, E 2 (estradiol), 17α,20β-P (17α,20β-dihydroxy4-pregnen-3-one) and P4 (progesterone) were evaluated by radioimmunoassay or ELISA. mRNA expression of hypothalamic gnrh-1, -2 (gonadotropin-releasing hormone-1, -2), pituitary gonadotropins ( fsh/lh , follicle-stimulating hormone/luteinizing hormone) and their cognate receptors ( fshr/lhr ) in ovaries were examined by qRT-PCR. Our findings demonstrated mRNA expression of hypothalamic sgnrh-1 , pituitary fsh and ovarian fshr increased in early ovarian development (360 DFH). Serum 17α,20β-P and pituitary lh mRNA expression first increased when trouts were in ovarian stage III (420 DFH). Ovaries were at different stages when reared in different densities. Long-term high density treatment (over 31.7 kg/m 3 ) resulted in decreased hypothalamic sgnrh-1 , pituitary fsh , ovarian fshr , serum E 2 , and increased hypothalamus gnrh-2 and serum dopamine during vitellogenin synthesis, suggesting HPG of rainbow trout might be retarded under dense rearing condition. [ABSTRACT FROM AUTHOR]