ID 41178
title alternative
An Ecological Study on the So-called Mogai (Anadara subcrenata (LISCHKE)) cultured in Kasaoka Bay
Ting, Yun-yuan
Kasahara, Shogoro
Nakamura, Nakaroku
Fishing industry. Fisheries
(1) 笠岡湾大島養殖場は,その水質(図2)および底質調査結果(表2,3)からみてモガイ養殖に好適な条件を備えている.
(2) 1年間(昭和45年5月~46年5月)のモガイの成長は,殼長についてみると,1年ものでは約0.8cmのものが3.4cm(増長分2.64cm)に達し,2年ものでは約2.7cmのものが4.8cm(増長分2.06cm)に成長した.
(3) 養殖場での全採集個体の計測値から得られた殼長と全重量,殼高及び殼幅の関係は,それぞれ図5,6及び7に示した通りである.
(4) 笠岡湾で1年養殖したもののうち,九州産種苗のものと大阪産種苗のものの形態について比較したところ,殼長と殼幅の関係における"位置"の差に有意性があり,同殼長の場合九州種は大阪種より殼幅の小さいことが認められたが,それは小型のものに顕著であった.
(5) 肥満度(肉重量/全重量)は,その値の低い8~12月の期間と1~7月の高い期間の二段階に大別された.雌雄別にみた肥満度は,年間を通した値では差はなかった(t=0.542<tα0.05=1.96)が,概して産卵期前は雌の方が高く,産卵期の後期およびそれ以後暫くは雄の方が高い値を示した.
(6) 笠岡湾養殖場におけるサルボウの生殖巣について,その発達過程を時期的に大別すると,1月から4月までは全体的に生殖細胞増殖期(生長前期,後期)に当り,5月から次第に成熟期に移る.6月から放出期個体の出現が見られ,7,8,9月は放出期に当るとともに,8月から放出後の濾胞期のものが増加し,それらは年末にかけて次第に次の生殖細胞増殖期に移行する.
(7) 笠岡湾養殖場における産卵期は6月から12月までの長期間に及ぶが,産卵盛期は7月から9月まである.
(8) 上記調査結果における生物学的最小形は雌雄とも殼長約1.5cm,重量約1.0gであり,また,産卵期間における性比は1:1であると認められた.
(9) 本種の放卵放精の誘発は,温度,精子懸濁液(放卵のみに対し),NH40Hによる刺激は何れも有効なことが認められたが,NaOH,KNO3の場合は無効であった.これらの反応に対する塩分条件の関係をみたところ,Cl14.08~24.40‰においては特にその影響はみられなかったが,Cl8.16および26.00‰においては誘発反応は阻止される.
(10) 殼長3~5cmの大きさのものの産卵数は大体500~1,000万個である.卵の大きさは直径51.38±3.78μである.
(11) 未受精卵を各塩分段階中に置いた場合,その受精および発生の能力はCl16.6‰前後の場合に最も長時間(22℃において,約13時間)保有されると認められる.
(12) 受精卵の発育に対する塩分条件は,D状ラーバに達するまでの歩留りからみるとCl15‰前後が最も適していると認められる.
The so-called "Mogai", Anadara subcrenata (LISCHKE) (a kind of ark shell) is one of the most important bivalves in the Seto Inland Sea, but in recent years the area of its culturing grounds is gradually decreasing due to reclamation works and water pollution through the release of industrial wastes. This study was carried out mainly to clarify the environmental conditions of Mogai culturing grounds in Kasaoka Bay, Okayama Prefecture; the growth of Mogai as well as the maturation of gonad; the artificial inducing of spawning and the effect of chlorinity upon the fertilization and the early development. The results obtained are as follows:

(1) Several items on the quality of water and bottom mud are shown in Fig. 2 and Table 2 & 3, signifying the fitness of the ground as to the culturing of this species.
(2) The growth of shell length in one year period from May 1970 on was from 0.8 cm to 3.4 cm and from 2.7 cm to 4.8 cm in the one year old and two years old classes respectively.
(3) The relations between shell length and total weight, shell height and also shell width which were calculated on the data obtained in 2,300 of cultured individuals are shown in Fig. 5, 6 and 7 respectively.
(4) The shell width of Mogai derived from Kyushu was smaller than that from Osaka at the same size, particularly in their young stage.
(5) The seasonal variation in fatness can be divided roughly into two periods, namely one from August to December when its evaluation is considerably low, and another from January to July. The difference of the evaluation of fatness between both sexes was not recognized.
(6) Microscopic photographs of gonads of both sexes in each stages of development are shown in Fig. 12.
(7) The spawning season seemed to happen from June to December. In the examined district, it was especially flourishing from July to September.
(8) The biological minimum of this clam was about 1.5 cm in shell length and 1.0 g in weight in both sexes. Sex ratio observed in spawning season was 1:1.
(9) The discharge of sexual products of this species was effectively induced by treatments of raising the water temperature, immersion in sperm suspended sea water (only to egg discharge) or suitable concentration of ammoniated sea water, but treatment by NaOH and KOH was not effective.
In regard to the influence of chlorinity upon the discharge of sexual elements, no particular effect was observed in the range of Cl 14.08‰ to 24.40‰. However, discharge reactions were obstructed in chlorinity of 8.16‰ and 26.0‰.
(10) Mogai of 3-5 cm in shell length discharged about five to ten millions eggs, the average diameter being 51.38±3.78µ.
(11) On the treatment of unfertilized eggs in water of different grades of chlorinity, the eggs were safely kept the longest period (13 hours at 22℃) in chlorinity of about 16.6‰.
(12) It was recognized that about 15‰ of chlorinity suits best the development of fertilized eggs of this species as can be judged by the survival rate up to the D-shaped larvae.
journal title
Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University
Volume 11
Issue 1
start page
end page
date of issued
nii type
Departmental Bulletin Paper
HU type
Departmental Bulletin Papers
DCMI type
text version
Graduate School of Biosphere Science