Relation between the reproductive status and somatolactin cell activity in the pituitary of pejerrey, Odontesthes bonariensis (atheriniformes)

The aim of this study was to analyze the relationship between somatolactin (SL) expressing cells and the reproductive status in a multiple spawning fish, the pejerrey Odontesthes bonariensis. Somatolactin cells were identified in adults of both sexes by immunocytochemistry using a heterologous piscine antiserum. The area of the cells that showed immunoreactivity to SL (ir‐SL) was compared in specimens with different degrees of reproductive activity as inferred from histological examination of the gonads and calculation of the gonadosomatic index (GSI %). The results showed a significant difference between the area of ir‐SL cells of resting/regressing (62.9 ± 2.1 µm2) and sexually active/vitellogenic (76.8 ± 2.3 µm2) females and a significant positive correlation between the ir‐SL cellular area and the GSI % (P < 0.01 in both cases). In males, the correlation between the area of ir‐SL cells and the GSI % was not statistically significant. However, in those animals with the highest GSI % values, the ir‐SL cells appeared more numerous and showed an increase in the immunostained area when compared to individuals with lower GSI % values. The present morphological observations are in accordance with biochemical data obtained from other species and support the assumption that SL might be involved in the regulation of reproduction in fish. J. Exp. Zool. 293:492–499, 2002. © 2002 Wiley‐Liss, Inc.