Eastern little tuna,Euthynnus affinis(Cantor, 1849) mature and reproduce within 1 year of rearing in land-based tanks

Abstract

Eastern little tuna (ELT, Euthynnus affinis) is expected to see use as a novel aquaculture species due to its rapid growth and high economic value. In this study, closing of the complete life cycle of ELT in land‐based tanks was successfully carried out. Seed production of a first generation (F1) derived from wild‐caught ELT broodstock was conducted in 2010, 2011 and 2012. Survival percentages of F1 ELT at 365 days post hatching for the 2010, 2011 and 2012 year classes were 0.9%, 0.4% and 6.3% respectively. On average, F1 ELT were approximately 40 cm in total length and weighed 1500 g by the time they reached 1 year of age. Successful artificial induction of spawning was achieved in 1‐year‐old F1 ELT using a gonadotropin‐releasing hormone analogue (GnRHa). Induction of spawning was successful at the first administration of GnRHa in the 2010, 2011 and 2012 year classes. First spawning was observed at 4 or 5 days post implantation, which indicated that oogenesis and spermatogenesis progressed within 1 year of rearing in land‐based tanks. During spawning periods, the average number of fertilized eggs and the average number of hatched larvae per spawning event in the 2010, 2011 and 2012 year classes were 20,480 eggs day−1 and 177 larvae day−1, 39,423 eggs day−1 and 9347 larvae day−1, and 819,555 eggs day−1 and 674,445 larvae day−1 respectively. Therefore, it was concluded that both male and female ELT reared in land‐based tanks were capable of reproduction at 1 year of age.

Spawning induction and seed production of Eastern little tuna, Euthynnus affinis (Cantor, 1849), in the post- and pre-spawning seasons by hormonal treatment in a semi-closed recirculation system with elevated temperature

“…Although we did not investigate the growth rates of seedlings produced in this study, ELT seedlings produced in May 2013 in our rearing system reached a BW of nearly 2 kg and TL of 40 cm at 200 days after hatching in December 2013 when the temperature of natural seawater dropped below 20°C (Yazawa et al . ). Since juveniles that reach a TL of approximately 30 cm by the beginning of the low‐temperature season typically show high survival through the winter period (Takeuchi et al .…”

“…). We also successfully demonstrated completion of the ELT life cycle in 38‐m 3 land‐based tanks (Yazawa, Takeuchi, Amezawa, Sato, Iwata, Kabeya & Yoshizaki ).…”

“…We previously showed that GnRHa administration was required for spawning induction of ELT maintained in 38‐ and 70‐m 3 land‐based tanks (Yazawa et al . , ). We demonstrated that maturation and spawning of ELT in the tank required a temperature of at least 25°C (Yazawa et al .…”

Production of triploid eastern little tuna,Euthynnus affinis(Cantor, 1849)

“…However, we also showed that the death rate of triploids was significantly higher than that of the diploids during the 2–4 weeks post‐hatching period when both the triploids and diploids were reared in the same tank. During this developmental stage, ELT juveniles showed high mortality due to their piscivorous behavior and cannibalism (Yazawa et al, ). Since triploid ELT could survive when reared individually (data not shown), it is speculated that triploid fish were selectively attacked by diploid fish.…”

“…Recently, ELT has attracted considerable attention as an alternative for the conventional aquaculture species in Japan due to its high commercial value and high growth performance. In previous studies, we developed the technique for the induction of natural spawning by the administration of gonadotrophin‐releasing hormone agonist (GnRHa) to ELT broodstock (Yazawa et al, ) and also successfully demonstrated completion of the ELT life cycle in a land‐based tank (Yazawa et al, ). Moreover, we have established a method for the stable and year‐round production of ELT seed by GnRHa administration (Yazawa et al, ).…”