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 (200 MU) at each head of the channel of Y-maze. Then 3 non-toxic hatchery-reared juveniles (body length, 5.6 ± 0.4 cm, n = 18) were released into the Y-maze and pecking behavior to carrier was observed for 3 h. The same procedure was tested for olfactory ablated juveniles and for juveniles received sham operation. Juveniles showed significant selectivity to TTX, except for olfactory ablated juveniles. These results indicate that pufferfish detects TTX by olfactory organ.
Tuna (genus Thunnus), particularly Pacific bluefin tuna (T. orientalis; PBT), are commercially important fish in the aquaculture industry worldwide. The objective of this study was to investigate sexual dimorphism in the growth performance of aquaculture-produced PBT and develop techniques for its sex manipulation, for the first time in tuna. A comparison of the body size between sexes revealed that male-cultured PBTs were larger than females at harvest. We also confirmed that cyp19a1a (encoding a gonadal aromatase) expression increased specifically in the genotypic female PBT gonads during sex differentiation. This suggested that aromatase plays an important role in ovarian differentiation and that the suppression of aromatase activity may effectively induce masculinization in genotypic females. Therefore, we administered letrozole—an aromatase inhibitor (AI)—into sexually undifferentiated PBT through the oral route. AI administration resulted in a 100% sex reversal of genotypic females into phenotypic males at the molecular level. Our results provide the basis for future studies on the establishment of mono-sex male production technology in PBT, which would help improve the productivity of closed-cycle PBT aquaculture. Furthermore, this study offers important insights into the understanding of the sex-wise growth of tuna species in aquacultural settings, and developing sex manipulation techniques.
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, 4.7-9.4 cm). TTX was detected in the same tissues as wild juveniles and epithelial cell layer of intestine of hatchery-reared juveniles (BL, 5.0-5.3 cm) 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.
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