A comparative study investigating the effects of food level and stocking density on growth and survival of larvae was conducted with yellowfin tuna (YFT) Thunnus albacares at the Achotines Laboratory, Inter-American Tropical Tuna Commission (IATTC), Republic of Panama , and Pacific bluefin tuna (PBF) Thunnus orientalis at Oshima Station, Kindai University, Japan, in May and July of 2023.
Larvae of each species were tested during the first 10 days of feeding (DOF) under replicated combination treatments of low and high food levels (500 rotifers/L and 5000 rotifers/L), and low and high initial stocking densities (5 larvae/L and 15 larvae/L) . The replicated treatments were: High F ood: Low Density (HF:LD ); Low F ood: Low D ensity (LF:LD); High F ood: High D ensity (HF:HD); and Low F ood: High Density (LF:HD).
Larvae were sampled on 1 DOF, 6 DOF and 11 DOF, and measurements of standard length (SL), and dry weight (WT) were obtained . On the last day of the experiment , all individual larvae from each tank were manually counted and an estimation of expected survival rate and standardized biomass of each treatment cohort were made.
With YFT larvae , both food level and density significantly affected growth in SL and WT (ANOVA, P < 0.01) . With PBF larvae , however, only food level significantly affected final SL and WT (ANOVA, P < 0.01), and density only affected growth significantly when interacting with food level (P = 0.016) . At all treatment levels except the LF:HD level, specific growth rate (SGR) in dry weight was higher for YFT compared to PBF and ranged from 28-33%/d, while SGR for PBF ranged from 27-30%/d. In the LF:HD treatment, SGR in dry weight was nearly the same for both species (23-24%/d). Survival rates on DOF 11 were higher for YFT compared to PBF over all treatments , and ranged from 5 -22%, including a surprisingly-high level of 20% at the LF:LD treatment. For YFT, there were statistically significant differences in final survival among treatments (ANOVA, P< 0.05), and stocking density significantly affected final survival . Over all treatments, mean survival at DOF 11 for PBF ranged from 4-14% , and no significant differences in survival were detected among food treatment s, although food level had a stronger e ffect than density on survival . With both species, only food level had a significant effect on standardized biomass of the cohort ( ANOVA, P < 0.05) .
Food level strongly affects growth of both species , with stocking density exhibiting a pronounced effect on YFT survival. YFT exhibit surprisingly strong survival and growth under low density conditions. Both species show high potential as candidate species for marine aquaculture.