Head Deformity in Tunas Kept in the Aquarium

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Details of morphological changes in tunas kept in confinement, have rarely been reported.The present paper reports on deformities appearing on heads of 3 species of tunas kept in an aquarium up to 172 days: Sarda orientalis, 5 specimens 314-340 mm in fork length and kept for 1-56 days;Euthynnus affinis yaito, 11, 272-382 mm, 10-72 days;Thunnus thynnus, 4, 229-328 mm, 1 51 days.The water, in a nearly closed system, was led by an inlet-pipe into the tank at the rate of 100 l/min, and was accelerated by two airlifting pipes in the tank.A translucent acryl-resin plate was inserted along the wall to prevent injuries to the fishes (Fig.1).The fishes were initially fed with chopped raw meat of the horse mackerel followed by the meat of penaeid shrimp;the daily ratio was under 20% in weight of tunas. The deformation appeared as a swelling of the skin in the head region excepting a triangular area posterior to the eye (Fig.3).The feature of the deformity showed specific differences but were similar among individuals of the same species.The swelling of the skin was especially prominent on the snout to nape, and on the branchiostegal membrane.The deformity appeared earlier in the period of confinement and with more prominent skin swelling in the order of Sarda, Euthynnus, and Thunnus (Fig.2).Macroanatomical observation revealed that the swelling of the skin was caused by thickening of the dermis accompanied by some development of lumps of the subcutaneous adipose tissue (Fig.4). Often, the periosteum of the membrane bones near the ventral border grew rough, associated with the development of adipose tissue, which coagulated with the periosteum.Among factors leading to the deformity of head, the confined space in which specimens were kept was believed to be highly responsible, because it was experienced that the same species of the tuna kept in round tank (6 m in diameter;holding capacity 31 m3;surface area 25.5 m2) showed similar head deformation but in lesser extent during more extended periods. Additional discussion is made on the author's experience and other information concerning Engraulis japonica, Scomber japonicus, Scomber scombrus, Coryphaena hippurus, Trachurus japonicus, Alectis cilialis, Seriola quinqueradiata, and Seriola purpurascens.All are neritic pelagic species and show similar deformation in head when kept under confinement.Feeding, vitamin difficiency, flowing of water, surface area of tank etc., also play important roles in morphological abnormalities of fishes reared in tanks.
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Head Deformity in Tunas Kept in the Aquarium

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日本魚類学会 | 論文

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