Metaplasia in swim bladder epithelium of the endangered annual fish Austrolebias nigrofasciatus (Cyprinodontiformes: Rivulidae) results in inadequate swimming and delayed growth

ABSTRACT Laboratory breeding of annual fish is often impaired when fish fail to inflate the swim bladder after hatching. These fish, which are known as belly-sliders, cannot swim in the water column, moving mainly on the bottom of water. Therefore, we wanted to understand the factors underlying failed inflation of swim bladder in the annual fish Austrolebias nigrofasciatus and determine the implications of this condition on the growth of juveniles. To identify how the initial filling of the gaseous vesicle is compromised, and to determine the implications of this condition on juvenile growth, we analysed the histology of the swim bladder of both normal swimming fish and belly-sliders during their initial growth phase (first month of life). In addition to slower growth rate compared with fish swimming normally, we found that belly-sliders have metaplasia characterized by epithelium peeling of the swim bladder and the presence of haemorrhage. Based on our findings, it can be concluded that metaplasia of the swim bladder is recurrent in annual fish bred in the laboratory, which explains the large number of unviable larvae. However, its causes remain unknown.

摘要：实验室繁育一年生鱼类时，常因幼鱼孵化后无法完成鱼鳔（swim bladder）充气而导致繁育受阻。这类被称为腹滑个体（belly-sliders）的幼鱼无法在水层中自由游动，仅能在水底移动。因此，本研究旨在阐明一年生鱼类黑带澳氏鱂（Austrolebias nigrofasciatus）鱼鳔充气失败的潜在机制，并明确该异常状态对幼鱼生长的影响。为探明鱼鳔初始充注过程受何种因素干扰，并明确该异常对幼鱼生长的影响，我们对正常游泳个体与腹滑型个体在初始生长阶段（孵化后首月）的鱼鳔组织开展了组织学分析。研究结果显示，与正常游泳的幼鱼相比，腹滑型个体不仅生长速率更为缓慢，还出现了以鱼鳔上皮脱落和出血为特征的上皮化生（metaplasia）。基于上述发现，可以得出结论：实验室繁育的一年生鱼类中，鱼鳔上皮化生现象频发，这也是大量幼鱼无法存活的核心原因。不过该现象的具体成因目前仍未明确。