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It has been shown that the common Japanese conger, Conger myriaster, may spawn several times rather than once in its lifetime. However, knowledge of their spawning ecology, including the age at which they spawn, is limited. Therefore, in this experiment, we compared the annual changes in the gonadal development between the second and third year of rearing fish in order to determine how different ages of the common Japanese conger affect in gonadal development under rearing conditions. As in the second year of rearing, the GSI of both males and females in the third year of rearing reached a maximum during the summer when the water temperature was rising, and the egg diameter of the females was also maximum. However, in the third year of rearing, GSI was lower in most months than in the second year of rearing, and there were significant differences in March, May, and October. Egg diameter was significantly higher in the third year of rearing in May and June, and the maximum annual egg diameter was also higher in the third year of rearing. Although there were distinctive changes in oocyte diameter composition and oocyte maturity stage in each year of fish, it was not possible to determine whether maturity was more advanced in any of the year of fish. It is necessary to compare the two age groups by actually inducing maturation in the future.

1976年4月から1977年12月までの期間，伊勢湾および熊野灘沿岸海域で得られた2,094個体のマアナゴの標本について，形態学的検討および食性についての研究を行い，概略次のような知見を得た。 1. 伊勢湾と熊野灘のマアナゴにつき，魚体各部位の相対成長の関係式を求め有意性の検定を行った。その結果，体重，体高，体幅 頭長などの全長に対する相対成長の式において有意の差が認められる。 2. マアナゴの全長組成は伊勢湾で200～400mm，熊野灘で300～600mmにモードがみられ，このモードには時期的な変化はみられないようである。3. マアナゴの脊椎骨数は伊勢湾で137～150，熊野灘で136～152，であり，両者の間に有意な差は認められない。4. 伊勢湾のマアナゴはスジハゼ，コモチジャコ，その他を，また熊野灘のそれはニギス，アオメエソ，センハダカなどを捕食し，生息水域による餌料の差を反映している。また摂餌量指数にはマアナゴの成長にともなう変化はみられず，αの値にも特に変化は認められない。, Common Japanese conger, Conger myriaster, is a valuable species as a food fish which occurs in the waters of Japan from southern part of Hokkido to Nansei-Islands and in the coastal waters around Korea-Peninsula. The fish is one of the important fishery resources in Ise-Bay and Kumano-Nada, where it is caught by means of long line,trawl net and trap net. The present report deals with the fishery biology of the Common Japanese conger, particularly with reference to morphometrical characters and feeding habit. The materials examined consist of 2,094 individuals taken from coastal areas of Ise-Bay and Kumano-Nada during the period from April 1976 to December 1977. The results obtained are summarized as follows : 1) The tests of significancy of relative growth equations are compactly summarized in Table 3. From results, it is clear that there were significant differences between Ise-Bay and Kumano-Nada with respect to morphometrical characters such as rations of body weight, body height, body width and head length to total length. 2) The mode of total length ranges 200-400 mm in Ise-Bay and 300-600 mm in Kumano-Nada. A obvious growth trend was not recognized from the monthly total length frequency distribution in each of the two areas. 3) Significant difference were not found in vertebral counts between the congers of Ise-Bay and Kumano-Nada. 4) Feeding habits were unquestionably different between the congers of Ise-Bay and Kumano-Nada. The former feed on Acentrogobius pflaumi, Chaeturichthys sciitius and others, while the latter on Glossanodon semifasciata, Chlorophthalmus albatrossis, Diaphus suborbitaｌis and the like.