Hideki Yamazaki

Puffer smells tetrodotoxin

Behavioral observation was conducted to test whether olfaction is functional to detect tetrodotoxin (TTX) in tiger puffer Takifugu rubripes using Y-maze. We placed either agarose carrier or one agarose and one agarose containing TTX (200xa0MU) at each head of the channel of Y-maze. Then three non-toxic hatchery-reared juveniles (body length, 5.6xa0±xa00.4xa0cm; nxa0=xa018) were released into the Y-maze and pecking behavior to carrier was observed for 3xa0h. The same procedure was tested for olfactory-ablated juveniles and for juveniles taht received sham operation. Juveniles showed significant selectivity to TTX, except for olfactory-ablated juveniles. These results indicate that pufferfish detects TTX by olfactory organ.

Evaluation of Stocking Effectiveness of the Japanese Spanish Mackerel in the Eastern Seto Inland Sea, Japan

This study evaluated the stocking effectiveness of two release groups of Japanese Spanish mackerel, Scomberomorus niphonius, in the eastern Seto Inland Sea, Japan. Juveniles of about 40 mm in total length (TL) that were directly harvested from seed production tanks and 100 mm TL that were reared in nursery facilities were released from early June to early July. The otoliths of released juveniles were marked with alizarin complexone. In 2002, 51,000 40-mm and 82,929 100-mm juveniles and, in 2003, 94,000 40-mm and 77,193 100-mm juveniles were released. A total of 2,761 individuals were sampled at the 14 main fish landing markets between 2002 and 2004, from September in the release year to June the next year. Recapture rates, yields from the released juveniles, contribution rates to the commercial landings, and the economic efficiency were estimated with standard errors. The variance estimators were derived by assuming simple random sampling of the commercial landings. All estimates for evaluating stocking effectiveness showed significantly higher values in the 100-mm release group than in the 40-mm release group. Consequently, releasing 100-mm juveniles reared in nursery facilities was more efficient than direct release of 40 mm juveniles.

Comparison of the localization of tetrodotoxin between wild pufferfish Takifugu rubripes juveniles and hatchery-reared juveniles with tetrodotoxin administration.

To reveal the accumulation profile of tetrodotoxin (TTX) in pufferfish Takifugu rubripes juveniles, we compared the localization of TTX in various tissues among wild juveniles and hatchery-reared juveniles with or without TTX administration using immunohistochemical technique with anti-TTX monoclonal antibody. Immuno-positive reaction was observed in hepatic tissue, basal cell of skin and olfactory, olfactory epithelium, optic nerve and brain (optic tectum, cerebellum, medulla oblongata) of wild juveniles (body length: BL, 4.7-9.4xa0cm). TTX was detected in the same tissues as wild juveniles and epithelial cell layer of intestine of hatchery-reared juveniles (BL, 5.0-5.3xa0cm) to which TTX was orally administrated. No positive reaction was observed from the tissues of hatchery-reared juveniles without TTX administration. These results suggest that orally administrated TTX to the non-toxic cultured juveniles is accumulated in the same manner of wild juveniles. In addition, our study revealed that pufferfish accumulates TTX in the central nervous system.

Administration of tetrodotoxin protects artificially raised juvenile tiger puffer Takifugu rubripes from predators

We examined the effects of tetrodotoxin (TTX) administration on artificially raised tiger puffer Takifugu rubripes juvenile survival after release into a mesocosm with predators to clarify the ecological significance of TTX. Pellets containing three different concentrations of TTX [0 as the control, 7 and 14xa0mouse units (MU)/g diet] were fed to non-toxic artificially raised T. rubripes juveniles for 10xa0days. TTX accumulation in the various tissues of fish was detected except for in the control diet group. TTX administration did not affect survival or growth of the fish. One hundred fish from each diet group were released together after TTX administration into a salt pond mesocosm (2650xa0m2) with predators (Lateolabrax sp.) for 5xa0days. Survival after release was significantly higher in both the fish fed with the 7xa0MU TTX/g diet (62%) and the 14xa0MU TTX/g diet (74%) than in the control fish (32%).

Effects of mother and postnatal food condition on larval performance of swimming crab Portunus trituberculatus

Seed production of the swimming crab Portunus trituberculatus in Japanese hatcheries frequently shows larval mass mortality because of abnormal morphologies and nutritional deficiencies. We conducted two laboratory experiments to explore the optimal food conditions for larval culture in this species. In experiment 1, hatchlings of three mothers were separately reared under different supplementation densities of digestible Nannochloropsis oculata for feeding to the Artemia nauplii provided to larvae. In experiment 2, hatchlings of three other mothers were separately reared under different supply densities of Artemia nauplii that had been cultured with different densities of digestible N. oculata. To evaluate larval performance, we examined larval morphogenesis and measured somatic growth of the carapace, starvation tolerance, development rate, and metamorphosis success. The food conditions significantly affected larval morphogenesis and growth. Additionally, we found large differences in many larval traits among the larvae hatched from different mothers. The food condition for achieving better survival differed among broods; thus, the optimal food conditions varied for larvae of different mothers. We conclude that seed-production success or failure depends largely on a match or mismatch between larval culture methods and characteristics conferred by the mothers used.