Growth indices of small northern bluefin tuna ( Thunnus thynnus, L.) in growth-out rearing cages

Abstract

The principal objective of the paper is to describe the growth pattern of small northern bluefin tuna ( Thunnus thynnus) in floating cages in the Adriatic Sea. For this purpose, several sampling and tagging experiments on live small tunas (mean weight: 10.47 ± 5.817 kg) in various growth-out floating cages were carried out during different rearing periods. Length and weight data of live fish were analyzed at sampling and tagging time, and recapture data eventually at harvesting time. Based on the obtained data condition parameters ( K), specific growth rates (SGR) and relative growth rates (RGR) and thermal growth coefficient (TGC) were calculated. Additionally, weight–frequency distributions at sampling and harvesting time are compared. It was observed that biomass of tagged fish, as a consequence of post-tagging related stress, decrease due to starvation (SGR < 0), although fish were able to recover to initial biomass (SGR = 0) within 2–3 months. Significant differences in K between wild tuna (1.95 ± 0.136) and farmed tuna (2.33 ± 0.216) were noticed. Also, no significant increase of K-value between tagged tunas (2.12 ± 0.246) and recaptured tunas (2.21 ± 0.231) in the rearing cages was noticed. However, after rearing for extended periods (> 1 year), one-year old tuna considerably increased their biomass (RGR % = 342.79). Such a production of tuna biomass using capture-based aquaculture, may satisfy increasing market demands without additional impact on fish mortality.