Reproductive Strategy of the Squid, Todarodes pacificus, Produce Large Gelatinous Egg Masses

通过野外调查和圈养实验，研究了与太平洋东乌贼种群波动有关的繁殖策略。未成熟的鱿鱼被收集并保存在一个环形槽中，在那里它们成熟、交配和产卵。凝胶状的卵团呈球形，几乎是浮力的。最大的鸡蛋直径为80厘米，含有大约20万个鸡蛋。卵团的表层有效地防止了甲壳类动物、原生动物和细菌的侵扰。在18-19℃的环境下，4-6天后孵化出幼虫，并积极游动，许多个体在水面上游动。卵群在孵化后不久就分解了。在3.5 ~ 29℃的温度范围内对卵和幼虫的存活率进行了检测，确定了发育和存活的最佳温度范围。15 ~ 23℃时胚胎存活率最高。结果表明，太平洋鳉鱼在温度高于15℃的环境中产卵，卵团在15 ~ 23℃的环境中会保持4 ~ 9.5天的结构，直至解体。据推测，太平洋鳉鱼在日本附近的产卵地点发生在15至23℃之间，并且在大陆架和斜坡之上，因为圈养的雌性通常在产卵前坐在水箱底部。自20世纪80年代末以来，日本太平洋蟾蜍的年捕获量逐渐增加。自1980年代末以来，副幼虫丰度也高于1970年代末和1980年代中期。基于不断变化的环境条件，我们提出了最近库存增加的可能情况。首先，我们研究了鱼类种群和幼虫捕获量的年变化趋势，并推断出潜在的产卵区域，假设卵群和孵化发生在15至23℃之间，并且在大陆架上。然后，我们根据GIS数据推断出1984-95年间产卵区域的变化。我们得出结论，自20世纪80年代末以来，秋、冬产卵区在对马海峡和后藤群岛附近重叠，冬产卵地点在东海大陆架和斜坡上扩展。少

Reproductive strategy related to stock fluctuation on the ommastrephid squid Todarodes pacificus are examined by field survey and captive experiments. Immature squid were collected and maintained in a raceway tank where they matured, mated, and spawned. Gelatinous egg masses were spherical and nearly buoyant. The largest egg mass measured 80 cm in diameter and contained approximately 200,000 eggs. The egg-mass surface layer effectively prevented crustaceans, protozoans, and bacteria from infesting the masses. Paralarvae hatched after 4-6 days at 18-19℃ and actively swam at once, with many individuals swimming at the surface. Egg masses disintegrated soon after hatching. Survival of eggs and paralarvae were examined at temperatures ranged from 3.5-29℃ to determine the optimum temperature range for development and survival. Highest embryonic survival rates occurred between 15 and 23℃. It is sugggested that T. pacificus spawns in waters warmer than 15℃, and egg masses maintain their struc … More ture for about 4-9.5 days before disintegrating at temperatures between 15 and 23℃.The inferred spawning sites of T. pacificus around Japan are assumed that egg masses and hatchlings occur at temperatures between 15 and 23℃, and above the continental shelf and slope, because captive females regularly sit on the tank bottom just before spawning. Annual catches of Todarodes pacificus in Japan have gradually increased since the late 1980s. Paralarval abundances have also been higher since the late 1980s than during the late 1970s and mid-1980s. We propose a possible scenario for the recent stock increase based on changing environmental conditions. First, we examined trends in the annual variations of stock and larval catches, and infer potential spawninig areas, assuming that egg masses and hatchlings occur at temperatures between 15 and 23℃, and over the continental shelf. We then infer changes in the spawning areas during 1984-95 based on GIS data. We conclude that since the late 1980s the fall and winter spawning areas have overlapped in the Tsushima Strait and near the Goto Islands, and that winter spawning sites have expanded over the continental shelf and slope in the East China Sea. Less