Otolith strontium : calcium ratios in a freshwater stingray, Himantura signifer Compagno and Roberts, 1982, from the Chao Phraya River, Thailand

Otolith microchemistry was examined in a freshwater stingray, Himantura signifer, collected from a freshwater region of the Chao Phraya River, Thailand. Otoliths of H. gerarudii and H. imbricata from the estuary at the mouth of the Chao Phraya River, and H. imbricata from the sea adjacent to the river mouth were also examined. Otolith Ca concentration was almost constant among the three species, regardless of their habitat environments. In contrast, Sr concentration and the Sr : Ca ratio differed considerably among the species, those of the freshwater species being at the lowest levels and that of the marine population of H. imbricata the highest. Intraspecific variation in Sr concentrations and Sr : Ca ratios found in H. imbricata from estuarine and marine environments suggested that those levels varied according to the habitat. Otolith Sr concentrations and Sr : Ca ratios of male freshwater stingrays increased with body growth, whereas those of female otoliths decreased temporarily to the lowest level in 250-300 mm disk width (mature) specimens. The findings suggested that H. signifer from freshwater regions enter a brackish or seawater environment at some time in their life history. The marked fluctuations in Sr concentration and Sr : Ca ratio in female otoliths may be related to presumed reproductive behavior, such as ceasing migration across a saline boundary during the reproductive period and giving birth in a freshwater region of the river, or may have been affected by changes in physiology and elemental metabolism associated with reproduction

サメ類の研究-20 : ホシザメとシロザメ胎児の腸管上皮細胞について

Electron microscopic observations were made on the epithelial cells of the intestines in Mustelus manazo and M. griseus embryos in order to examine their structure and function. The intestinal epithelial cells in the embryos of both species are characterized by microvilli on the free surface, intermicrovillous invaginations of the plasma membrane, and a number of vesicles, granules, and vacuoles. These characteristics suggest that the intestinal epithelial cells in M. manazo and M. griseus embryos may be engaged in absorption. It has been clear that interdigitations of the lateral plasma membrane at the intercellur junctions, which are not seen in the intestine of teleostean fish, are observed to occur in the M. manazo and M. griseus embryos.ホシザメとシロザメ胎児を用いて,それらの腸管上皮細胞の構造と機能を電子顕微鏡的手法により究明した.両種の胎児の腸管上皮細胞は遊離表面上の微絨毛,微絨毛間の細胞膜の陥入,多数の小胞,空胞,顆粒等により特徴づけられる.これらの特徴により,ホシザメとシロザメ胎児の腸管上皮細胞は吸収細胞として機能すると考えられる.また,硬骨魚類の腸管上皮には見られない隣接細胞の側面および基底面の細胞膜のかみ合いの形成がホシザメとシロザメ胎児において観察された

Evidence for migration of metamorphosing larvae of Anguilla japonica in the Kuroshio

Two sampling surveys of the R/V Tansei Maru were conducted in the Kuroshio region south of Kyushu Island of Japan and to the south in the western North Pacific, to study the distribution patterns of the larval stages of the Japanese eel Anguilla japonica as they approach their recruitment areas in East Asia. Nine fully-grown premetamorphic leptocephali (49.5-58.3mm TL) were collected during November 1996 to the east of Taiwan. During November and December 2000, nine early stage glass eels (51.3-57.0mm TL, pigmentation stage II-IV) that were still in the late metamorphosis stages were collected in the Kuroshio. These findings suggest that metamorphosing Japanese eel leptocephali that recruit to the northern part of their species range migrate in the Kuroshio. They may detrain from the Kuroshio at the pigmentation stage IV-VA and begin their coastal migration

Eel cruise V

航海番号: KH-91-4 ; 航海日程: June 14 - July 22, 199

Eel cruise V

航海番号: KH-91-4 ; 航海日程: June 14 - July 22, 199

Otolith strontium : calcium ratios in a freshwater stingray, Himantura signifer Compagno and Roberts, 1982, from the Chao Phraya River, Thailand

Otolith microchemistry was examined in a freshwater stingray, Himantura signifer, collected from a freshwater region of the Chao Phraya River, Thailand. Otoliths of H. gerarudii and H. imbricata from the estuary at the mouth of the Chao Phraya River, and H. imbricata from the sea adjacent to the river mouth were also examined. Otolith Ca concentration was almost constant among the three species, regardless of their habitat environments. In contrast, Sr concentration and the Sr : Ca ratio differed considerably among the species, those of the freshwater species being at the lowest levels and that of the marine population of H. imbricata the highest. Intraspecific variation in Sr concentrations and Sr : Ca ratios found in H. imbricata from estuarine and marine environments suggested that those levels varied according to the habitat. Otolith Sr concentrations and Sr : Ca ratios of male freshwater stingrays increased with body growth, whereas those of female otoliths decreased temporarily to the lowest level in 250-300 mm disk width (mature) specimens. The findings suggested that H. signifer from freshwater regions enter a brackish or seawater environment at some time in their life history. The marked fluctuations in Sr concentration and Sr : Ca ratio in female otoliths may be related to presumed reproductive behavior, such as ceasing migration across a saline boundary during the reproductive period and giving birth in a freshwater region of the river, or may have been affected by changes in physiology and elemental metabolism associated with reproduction

土佐湾及び四国沖黒潮流域で採集されたウナギ目魚類レプトケファルス幼生の分布

土佐湾及び四隅沖黒潮流域で、1990年1月にウナギ目魚類レプトケファルス幼生の採集を行った。採集は丸稚ネット(口径1.3m、網口面積1.33㎡、目合O.33mm)による傾斜曳あるいはステップ曳と高速稚魚ネット(網口面積2.03㎡、目合2.0mm)による表層曳で行われた。計41尾のレプトケファルス幼生が黒潮流域で採れた。その内訳はギンアナゴGnathophis nystromi nystromi(JORDAN et SNYDER)(33尾)、ニラミアナゴ属sp. 5 Ariesoma sp. 5(1尾)、ニラミアナゴ属sp. 7 Ariosoma sp. 7(2尾)、クロアナゴConger japonicus BLEEKER(1尾)、クロアナゴ亜科sp. 1 Congrinae sp. 1(2尾)、メクラアナゴDysomma anguillare BARNARD(2尾)であった。全個体の82.9%(34尾)が黒潮南外側域に分布していた。またギンアナゴは全個体が表層曳で、それ以外は全でステップ曳(ワイヤー長;500, 400, 300, 200, 100m)で採集された。A total of 41 leptocephali was collected in the Kuroshio waters off Shikoku Island. They included 33 Gnathophis nystromi nystromi (JORDAN et SNYDER), one Ariosoma sp. 5, two Ariosoma sp. 7, one Conger japonicus BLEEKER, two Congrinae sp. 1, and two Dysomma anguillare BARNARD. Most of leptocephali collected (82.9% of a total catch) were occurred in the southern boundary of the Kuroshio Current. All the Gnathophis leptocephali were collected with the surface horizontal tow of High Speed Larva Net, and the other leptocephali were with step tow of Larva Net