マダイ養殖の基礎的研究-IV : 稚子の疾病について(2)鰾の異常膨満

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In the rearing of artificially hatched Chrysophrys major numerous cases of larval fish with abnormal expansion of the swimbladder were observed between 10 to 15 days after hatching. The oxygen content of the aquarium water in which the larvae were reared was normal (5.1-6.1cc/L). Abnormal expansion of the swimbladder was due to an abnormally large amount of gas in the swimbladder (Figs. 1-3). The long-diameter of the distended swimbladder was about 1/10th of the total length of the body. That of a normal swimbladder is about 1/20th (Table 1). The existence of gas in the swimbladder was recognized in an estimated 40% of the larval fish 9 days after hatching, and in 100% 11 days after hatching. The swimbladder of the young fish up to 8 days after hatching seems to contain sea water in the normal condition. In the larva of Chrysophrys major the development of the gas gland of the swimbladder and the closing of the pneumatic duct occur between 8 to 10 days after hatching (Figs. 9, 10, 12). This period seems to be physiologically insecure for the young fish.
公益社団法人日本水産学会の論文