実験動物としてのブルーギルサンフィッシュに関する研究 : II. 卵内発生と稚仔の成長

Studies on the Usefulness of the Bluegill Sunfish，Lepomis macrochirus Rafinesque，as an Experimental Standard Animal : II. On the Developmental Stages and Growth from the Egg through One Year

Nakamura Nakaroku

Kasahara Shogoro

Yada Toshiaki

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

Bluegill sunfishを実験動物として用いるための研究の一部として周年採卵を目的とした研究を行なっているが，その基礎資料として産卵習性に引続いて卵内発生，仔魚の成長及び0年魚の成長等について実験観察を行なった.

(1) 卵は直径1.23mm前後の粘着卵で，卵黄には1個の大油球(約0.38mm)と多数の小油球がある.
(2) 卵径は個体により，また同一個体でも産卵の度に変異があるが，親魚の年令，大きさ，産卵回数，産卵数等との間には一定の関係は見出されなかった.
(3) 水温24.5±1.0℃での孵化期間は平均40時間(37～43時間)，28.5±1.0℃では28時間(27～29時間)，18.5±1.0℃では79時間(75～85時間)であった.18.5℃のものは46%もの奇形率を示した.なお上記の3段階の水温での卵内発生の経過はTable 2に示した.
(4) 人工採卵によって得た卵の受精率，孵化率は自然産卵のものに比べてかなり低かった.
(5) 孵化仔魚は全長3.23mmで1.13×0.9mm位の卵黄を残し，体のどの部分にも色素胞の出現は見られない.
(6) ミジンコ類は最も適した初期餌料で，それによる成長はコペポーダ，輪虫によるものより速かであった.全長13mm位で鰭の棘，軟条の定数が現われ，14-15mmで鱗が出来，縞も認められる.
(7) 稚魚の全長瀕度分布曲線の検討によってトビの現象は認められないことが判った.
(8) 満1年で体長約5.3cm(3.0-8.3cm)に成長するが，雄は雌に比べて大きい.

As part of research-work on the usefulness of the bluegill sunfish, Lepomis macrochirus Rafinesque, as an experimental standard animal in fisheries research, we have tried to find out a way of obtaining its fingerlings throughout the year-curriculum. In sequence to the previous study on the breeding habits, some examinations have been conducted mainly on the developmental stages and the growth from the egg till one year after the hatching, using spawned eggs by full three or four year old fish in rearing tanks. The results so far obtained are as follows:
(1) The egg is adhesive and spherical in shape, measuring about 1.23 mm in diameter, with one large oil-globule (ea. 0.38 mm) and many minute ones.
(2) The egg diameter varies in the individuals and also in the batches of the same fish. However, no certain relation was found between the egg diameter and the age, the size and the number of times of spawning of the mother fish nor with the number of eggs spawned.
(3) The incubation period was about 40 hours (37-43 hours) at a temperature of 24.5°C, 28 hours (27-29 hours) at 28.5°C and 79 hours (75-85 hours) at 18.5°C, respectively. However, abnormal larvae appeared in a fairly high percentage (ea. 46%) at a temperature of 18.5°C, which is considered nearly out of the optimum spawning temperature.
(4) A percentage of fertilization and hatching of the eggs taken by the artificial insemination was fairly lower than those of the natural spawning.
(5) The newly hatched larva is about 3.23 mm in total length, with a yolk of 1.13×0.9 mm in size and no pigment in any part of the body.
(6) Cladocera (Morina sp.) seems to be most adequate food in the early stages of the bluegill larva, those fed with them showed faster growth than those fed by rotifers or copepods.
(7) The definite number of the spine and ray of each fin appeared at a total length of 13 mm, after that the lateral striped pattern appeared on the body side with the complete formation of the scale at a size of 14-15 mm in total length.
(8) From the examination of the size-frequency of the reared fingerlings, it was recognized that the phenomenon of "shoot individual" does not occur.
(9) The first year's growth of the bluegills is about 5.3 cm (3.0-8.3 cm). The average rate of growth of the female is below that of the male.

Zoology [ 480 ]

jpn

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563

[NAID] 40018463802