池塘养殖牙鲆(Paralichthysolivaceus)无眼侧体色黑化消褪机理

Physiological Mechanisms for Degeneration of Blind-Side Hypermelanosis in Pond-Cultured Japanese Flounder(Paralichthys olivaceus)

针对池塘养殖牙鲆(Paralichthys olivaceus)无眼侧体色黑化消褪的现象,本研究从形态、血清和mRNA水平上对其生理学机制进行了研究。光镜观察显示,无眼侧消褪区域的黑色素细胞数量显著少于有眼侧和无眼侧黑化区域(P<0.05),电镜观察发现,无眼侧消褪区域皮肤中黑色素颗粒模糊,黑色素细胞中色素体存在凋亡现象。无眼侧黑化区域消褪过程中,鳞片类型经历了由栉鳞—弱栉鳞—圆鳞转变的过程,栉鳞上硬棘数量也随之减少。无眼侧黑化消褪的牙鲆血清中的黑色素聚集激素(MCH)肽含量显著高于无眼侧正常和无眼侧黑化的牙鲆(P<0.05),但无眼侧体色黑化的牙鲆血清中的黑色素细胞刺激激素(MSH)肽含量显著高于其他2种类型的牙鲆(P<0.05)。基因表达分析显示,无眼侧黑化消褪鱼垂体MCH mRNA表达水平显著高于无眼侧黑化鱼(P<0.05),而垂体POMC1 mRNA表达水平显著低于无眼侧黑化鱼(P<0.05),但都与无眼侧正常鱼无显著差异。研究结果可为阐释池塘养殖牙鲆无眼侧体色黑化调控机制提供理论支持。

Blind-side hypermelanosis is a serious problem among intensively cultured Paralichthys olivaceus, resulting in significant economic losses. To date, no treatment is available to prevent this problem due to lack of knowledge. However, the degeneration of blind-side hypermelanosis was observed among pond-cultured P olivaceus recently. To investigate the possible mechanisms, three types of P olivaceus were identified based on the pigmentation on the blind side： normal blind-side type （NBS）, blind-side hypermelanosis type （BSH）, and blind-side degeneration type （BSD）, and used for the comparison of morphological and associated endocrine changes at hormonal and mRNA levels. For BSD type, the number of melanocytes in the hypermelanosis-degenerated parts of blind side was reduced significantly comparing to those in the eye-side parts and in the blind-side parts in the BSD type. Moreover, the scales in the hypermelanosis-degenerated parts experienced the transformation from ctenoid to weak ctenoid, and cycloid shape. Meanwhile, the number of ctenoid scale spines on the blind- side decreased in hypermelanosis-degenerated parts among BSD fish. The plasma melanocyte-stimulating hormone （MSH） and melanin-concentrating hormone （MCH） levels were determined and compared between the three types of P olivaceus. Our results showed that the BSD plasma MCH level was significantly higher than that of NBS and BSH, whereas the BSH had the highest MSH level among all three types of fish. Gene expression analysis showed that the BSD pituitary MCH mRNA level was remarkably higher than that of BSH, but for POMC mRNA level, the BSD was significantly low. Results from the present study significantly improved the understanding of the hyperpigmentation on the blind- side ofP olivaceus and help to develop the protocol to control this problem in aquaculture production.