Male germ cell apoptosis in wild and captive bluefin tuna (Thunnus thynnus L.)

In the last decade, intense research has been carried out in an effort to domesticate bluefin tuna (Thunnus thynnus). Male bluefin tuna reared in captivity from one to three years have proven unable to undergo normal testicular maturation (Corriero et al., Aquaculture, 272, 2007). A short term treatment (3 to 8 days) with slow-release gonadotropin-releasing hormone agonist (GnRHa) implants was not sufficient to stimulate testicular maturation, but was effective in reducing germ cell apoptosis, a form of cell death involved in various physiological and pathological processes, including gametogenesis (Corriero et al., Anim. Repr. Sci., in press). The aim of this work was to investigate the effect of captivity-induced stress on male germ cell apoptosis in bluefin tuna. Testis samples were taken from 30 bluefin tuna reared in captivity in floating cages in Cartagena (Spain), Malta and Vibo Marina (Italy). For comparison, testis samples from 21 wild individuals were used. Tissue samples were fixed in 10% buffered formalin, dehydrated in ethanol and embedded in paraffin wax. Germ cell apoptosis was detected through the terminal deoxynucleotidyl transferase-mediated d’UTP nick end labelling (TUNEL) method. Apoptotic germ cells, both spermatogonia and spermatocytes, were found in all sampled observed. In captive fish, germ cell apoptotic rate was significantly higher than in wild individuals and further increased if repeated handling and sampling operations occurred in the rearing cage.