Lectin-binding pattern of developing oocytes in wild and GnRH-treated bluefin tuna (Thunnus thynnus)

Captive Bluefin tuna show disturbante in final oocyte maturation probably due to an altered endocrine process. In fish oocytes, the expression of glycoproteins is regulated by sexual hormones and has not been included yet among the markers for egg quality determination (Lahnsteiner et al.. Aquacolture, 195, 2001). This study detected thè glycoconjugate pattern in developing oocytes of wild and captive bluefin tuna by means lectin histochemistry. Ovarian fragments from adult bluefin tuna, wild or captive (control and GnRH-treated), were fixed in Bouin's solution, embedded in Paraplast and sections were stained using 13 lectins. Previtellogenic oocytes showed: a) nuclear staining with PNA and GSA II in wild tuna, with SNA, DBA, UEA I, and LTA in wild and GnRH-treated tuna, with MAL II, SBA, RCA120, HPA, Con A, WGA, GSA I-B4 in all the samples; b) edge of lipid droplets bound to SNA, PNA, DBA, GSA I-B4, GSA II, UEA I, LTA in wild tuna, to SBA in wild and treated tuna, to RCA120, Con A, WGA in all samples. Vitellogenic oocytes showed yolk globules periphery linked to PNA and GSA II in wild tuna, to HPA, GSA I-B4, UEA I, LTA in wild and treated tuna, to MAL II, SNA, DBA, RCA120, SBA, Con A, WGA in all the samples, These results suggest that the captivity somehow disrupts the glycoconjugates of bluefin tuna oocytes and that GnRH eases but does not eliminate the disorder.