Swim bladder malformation in hatchery-reared striped trumpeter Latris lineata (Latridae)

Abstract

Swim bladder malformation is common in both larvae and later life stages of cultured striped trumpeter Latris lineata. This study used histology and gross morphology of whole larvae to describe the progression of abnormal development that proceeded initial liquid dilation of the primordial swim bladder. In addition, radiography was used to compare swim bladder morphology of cultured juveniles with wild-caught specimens. The histomorphology of the swim bladder prior to lumenal dilation was typical of transient physostome larvae reported in the literature. A distinct swim bladder lumen present in larvae between 5.2–5.7 mm standard length (SL) was assumed to be liquid dilated and coincided with mouth opening. Initial gaseous inflation was first apparent when larvae attained 5.7–6.2 mm SL, after the resorption of the yolk sac and oil globule and the onset of first feeding (<5.5 mm SL). Successful gaseous inflation ranged between 0% and 75% in the cohorts of larvae examined. When gaseous inflation failed to occur, abnormal development proceeded in which the liquid dilated swim bladder collapsed, occluding the lumen. Hypertrophy of the swim bladder epithelium and hyperplasia of the rete mirable ensued. Radiography revealed that wild-caught striped trumpeter had a euphysoclist (dual-chambered) swim bladder, in which the chambers are separated by a diaphragm. In comparison, cultured juveniles and sub-adults displayed highly varied swim bladder morphologies, including apparently normal, malformed, and non-functional swim bladders in which a gaseous lumen was entirely absent. Kyphosis was inflicted in extreme cases of swim bladder malformation in which a distended single chamber both displaced the viscera and pushed the spine upwards. It was concluded that striped trumpeter larvae can be afflicted with swim bladder malformations consistent with cultured larvae of other transient physostomes; however, swim bladder malformation of later life stages of striped trumpeter is atypical in comparison to other literature reports and may be unrelated to the larval malformation described.