Spontaneous spawning of Atlantic bluefin tuna Thunnus thynnus kept in captivity

Abstract

Beginning 48-72 h after GnRHa treatment in 2009, massive spawning occurred for 17 days, with a daily maximum of 34 million eggs collected (SELFDOTT, 2010). On 17th June 2010 spontaneous spawning started in cage R2. From this day onwards and more or less daily viable eggs were obtained from both cages so no hormonal implants were used. Fish spawned intermittently for a period of 34 days in both cages, with a total of 58 million eggs collected. Cage R1 spawned for 26 days and produced 48 million eggs and cage R2 spawned for 28 days and produced 10 million eggs (Figure 1). As happened in 2009 (SELFDOTT, 2010), due to the almost non-existence of currents throughout the spawning period, almost all the eggs were collected at the surface, held by the plastic curtain. Only a small amount of eggs were captured by the egg collectors, which were designed to operate under current. Eggs were transported to the IEO facilities in Mazarrón (SE- Spain) where they were incubated. On average, the hatching rate was above 90%. No difference in hatching success was observed between 2009 (from hormonally treated cage) and 2010 (from spontaneously spawning fish).