Effect of water surface condition on survival, growth and swim bladder inflation of yellowfin tuna, Thunnus albacares (Temminck and Schlegel), larvae Tomoki Honryo 1 , Teruyoshi Tanaka 2, *, Angel Guillen 3 , Jeanne B. Wexler 4 , Amado Cano 3 , Daniel Margulies 4 , Vernon P. Scholey 4 , Maria S. Stein 4 & Yoshifumi Sawada 1 1 Oshima Branch, Fisheries Laboratories, Kinki University, Wakayama, Japan 2 Uragami Branch, Fisheries Laboratories, Kinki University, Wakayama, Japan 3 Aquatic Resources Authority of Panama, General Investigation and Development, Panama, Republic of Panama 4 Inter-American Tropical Tuna Comission, La Jolla, CA, USA Correspondence: T Honryo, Oshima Branch, Fisheries Laboratories, Kinki University. Oshima, Kushimoto, Wakayama 649-3633, Japan. E-mail: t.honryo@kindaisuiken.jp *Present address: Division of Vascular Surgery Department of Surgery University of Wisconsin-adison Madison WI USA Abstract Early-stage mortality due to surface water tension- related death and due to sinking to the tank bot- tom was investigated for yellowfin tuna, Thunnus albacares (YFT), larvae. Different aeration rates and rearing water surface conditions were examined to evaluate the effect on larval survival, swim bladder inflation and growth. The percentage survival of yolk sac larvae was significantly higher when the rearing water surface was covered with fish oil at aeration rates of 0 and 50 mL min À1 . The highest mortality occurred at the highest aeration rate of 250 mL min À1 regardless of surface water condi- tion. A second experiment was conducted twice under different water surface conditions: the water surface was covered by fish oil (FO), skimmed of fish oil (SS), and was not treated (NC). The per- centage survival was not significantly different between treatments after 7 days of feeding. In con- trast to the survival, the proportion of larvae with inflated swim bladders was significantly higher for the NC and SS groups than that of the FO group. Results of these experiments indicate that the addi- tion of oil to the rearing water surface without its removal interferes with the initial swim bladder inflation in YFT larvae. These results also indicate that YFT larvae need to obtain (gulp) air at the water surface for initial swim bladder inflation, and success of initial swim bladder inflation may be crucial for their survival. Keywords: yellowfin tuna, water surface, swim bladder, survival, mortality Introduction Tunas are one of the most valuable fish in the worldwide market. Among them, yellowfin tuna (Thunnus albacares; YFT) is the second-most abun- dant species in tuna catches and consumption in the world. FAO 2014 and the Fisheries Agency of Japan (2013) reported that 1239 K/T of YFT were caught worldwide during 2011, which accounted for 27.2% of the total catch of tunas. Atlantic (Thunnus thynnus) and Pacific bluefin tuna (Thun- nus orientalis; PBF) are now facing depletion of their wild populations (Cyranoski 2010). The total allowable catch of YFT is not strictly regulated compared with that of other tunas, despite the commercial importance of this fish. Therefore, increased fishing pressure may also result in deple- tion of this resource, thus it is important to inves- tigate factors that affect pre-recruit survival in YFT and the feasibility of aquaculture to mitigate the fishing impact on existing wild stocks of YFT. The Inter-American Tropical Tuna Commission (IATTC) is a pioneer in early life history research of this species and a large amount of biological information has been accumulated (Margulies, Scholey, Wexler, Olson, Suter & Hunt 2007a). The IATTC previously reported on the land-based broodstock management (Wexler, Scholey, Olson, © 2014 John Wiley & Sons Ltd 1 Aquaculture Research, 2014, 1–9 doi: 10.1111/are.12641