Physiological and ecological characteristics of diadromous fish in islands of the Pyukyus

本研究是为了阐明一些生活在琉球岛附近海域的二恶鱼的生理和生态特性。Ryukyu-ayu (Plecoglossus altivelis ryukyuensis)：该物种成熟精子的结构特征是细胞核对称，两个中心粒的排列不对称，与altivelis Ayu不同。鳞片、梳状鳞节、消化道和骨骼的发育早于阿玉。与ayu相比，上游迁移发生得更早（2月至3月），规模也更小（平均32.3毫米）。旗鱼（Kuhlia marginata）：根据组织学观察和性腺-体细胞指数，估计雌性在产卵期（4 - 9月）多次产卵。卵巢卵数随水深的增加在7万~ 36万个之间变化。幼鱼在水深约20毫米时由海洄游到河中，3 ~ 7月雌鱼的生长速度快于雄鱼。女性和男性的平均寿命分别为6岁和2岁，男女比例为3:1。血浆中Na和C1的变化表明鱼对环境盐分具有较高的耐受能力。罗非鱼（Oreochromis mossambicus）：罗非鱼是冲绳岛河口的主要鱼类。据估计，这种鱼的平均生育期为2-9年。每年的产卵期从5月持续到9月，雌性在这个季节可能会产卵几次。虽然对不同盐度条件下的氧耗率、血浆成分和血浆激素水平等生理参数的分析表明，海水可能是鱼的有利环境，但它们选择河口作为栖息地可能是基于物种繁殖策略的原因。

This study was carried out to clarify the physiological and ecological characteristics of some selected diadromous fish inhabiting sround the island of the Ryukyus.1.Ryukyu-ayu (Plecoglossus altivelis ryukyuensis) : The structure of mature spermatozoon of this species was characterized by a symmetric nucleus and asymmetric arrangement of two centrioles unlike Ayu, P.altivelis. Scales, comb-like teenth, alimentary canals and skeleton developed earlier than Ayu. Upstream migration also occurred earlier (February-March) and smaller in size (av. 32.3 mm) than Ayu.2.Flagtail (Kuhlia marginata) : Based on the histological observations and gonad-somatic index, it was estimated that females spawn repeatedly during the spawning period from April to September. Number of ovarian eggs varied between 70,000 to 360,000 with an increase of BL.After young migrated from sea to rivers at av. 20mm BL,during March to July, females grew faster than males. The average longevity of female and male was estimated 6 and 2, respectively, and the ratio of female to male resulted in 3 : 1. The change in plasma Na and C1 after trasfer to sea water revealed that the fish have the high ability of tolerance to environmental salinity.3.Tilapia (Oreochromis mossambicus) : The species O.mossambicus is the dominant fish occupying the estuaries of Okinawa Island. The average fertile span of this fish was estimated to be 2-9 years. Annual spawing period lasts from May through September, and females may spawn several times during this season. Although the analysis of the verious physiological parameters such as oxygen consumption rates, plasma constituents and plasma hormone levels under the different salinity conditions showed that sea water may be favorable environment to the fish, they might selsct estuaries as their habitat on the basis of the causes of reproductive strategy of the species.