An integrated approach to the conservation and management of the European eel in the mediterranean region: immunolocalization of steroidogenic enzymes during sex differentiation

Studies on steroidogenic cells producing key enzymes during sex differentiation are relevant for eel conservation and sustainable stock management. The enzymes cytochrome P450 side-chain cleavage (P450scc), 3-beta-hydroxysteroid dehydrogenase (3β-HSD) and aromatase (CYP450) play a key role in steroid metabolism. The immunolocalization of CYP450scc, 3β-HSD and aromatase, previously studied in some teleosts (Kobayashi et al., 1998; Bhandari et al., 2006), was investigated in wild European eels (Anguilla anguilla) from Valli di Comacchio, Ferrara (Italy). Sections of the entire gonad were exposed to goat polyclonal antibodies and prepared for optical microscopy (Grandi et al., 2003). The first steroidogenic cells, observed in undifferentiated gonads of 14-16 cm eels, did not show P450scc, 3β-HSD and aromatase activity, but a positive immunolocalization appeared at the same stage in cephalic kidney (interrenal) regions. Steroidogenic cells positive to all enzymes appeared in undifferentiated gonads of 16-20 cm yellow eels. Pre-Leydig steroidogenic cells, identified in Syrski organs of 22-28 cm yellow eels, were positive to 3β-HSD and P450scc, but negative to aromatase; however, steroidogenic cells identified in ovarian interstitial tissue were positive to all enzymes. In initial ovaries of yellow eels of the same length, some cells, identified as presumptive thecal cells, resulted positive to all three enzymes.Thus sex differentiation apparently shows an initial female stage, probably through control of aromatase activity. The immature testes of yellow and silver eels have large clusters of Leydig cells showing immunostaining with P450scc and 3β-HSD antiser