1,720,992 research outputs found
Temperature-dependent recruitment delay of the Japanese glass eel Anguilla japonica in East Asia
No full textMolecular Cloning and Sequence Analysis of the cDNAs for Pituitary Glycoprotein Hormone α Subunits from Two Species of Synbranchiformes, Monopterus albus and Ophisternon bengalense
No full textThe sex ratios and growth strategies of wild and captive Japanese eels Anguilla japonica
No full textTime series analysis in the catch of Japanese glass eels: possible effects of the reproductive cycle and an El Ni?o event
No full textVariable habitat use by Japanese eel affects dissemination of swimbladder parasite Anguillicola crassus
No full textDoes variable habitat usage by the Japanese eel lead to population genetic differentiation?
No full textGrowth and habitat residence history of migrating silver American eels transplanted to Taiwan.
No full textSex-dependent habitat use by the Japanese eel Anguilla japonica in Taiwan
No full textThe Japanese eel Anguilla japonica is a catadromous fish, but it has recently been discovered
that the use of freshwater habitat at the yellow eel stage is facultative. To determine if habitat
use by Japanese eels differs between the sexes we examined the strontium:calcium (Sr:Ca) ratios
in otoliths of 221 eels by electron probe micro-analyzer to reconstruct their environmental history.
Eels were collected from the Kaoping River estuary of southwestern Taiwan from 1998 through 2005.
The habitat use of yellow phase eels was divided into 3 types according to the life history pattern of
the otolith Sr:Ca ratios: Type 1 (freshwater resident), Type 2 (brackish water resident with a freshwater
preference) and Type 3 (brackish water resident with a seawater preference). Habitat use
differed significantly between male and female silver stage eels. Females were classified predominantly
as Type 2 or 3 while males were classified predominantly as Type 1 or 2. Consequently, female
yellow stage eels preferred an estuarine habitat while males preferred a freshwater habitat. In addition,
the mean otolith Sr:Ca ratios in the region 200 to 400 μm from the primordium (which corresponds
to the period of sex differentiation) were higher in females than in males. This indicated that
the sex differentiation of the eel might be related to habitat use, i.e. brackish water eels tended to differentiate
as females and freshwater eels as males
Gonadotropin Induced Synchronous Changes of Morphology and Gonadal Development in the Japanese Eel Anguilla japonica
No full textIn a previous study, we had observed synchronous changes of morphology and gonadal development in wild Japanese eel during the silvering process. In this study, we aimed to clarify if gonadotropin is the key hormone responsible for this phenomenon. Yellow eels captured in the Kaoping River were repeatedly injected with human chorionic gonadotropin (HCG), and changes of morphology and gonadal development were examined. After five weekly injection of HCG at a dosage of 0.75 IU/g body weight, eels was classified into well-responsive and poor-responsive groups according to skin coloration. Approximately 50 % of males and 20 % of females were responsive to become silver eels. Mean age, total length, body weight, condition factor, gonadosomatic index (GSI), fin-index (FI), hepatosomatic index (HSI) and ocular index (OI) were significantly higher in well-responsive eels than in poor-responsive eels. The mean digestosomatic index (DSI), in contrast, significantly decreased in well-responsive eels compared to poor ones. OI was positively correlated and DSI was negatively correlated with the GSI in both sexes. These results indicated that well developed eels are more sensitive to HCG treatment, and the skin color, eye size, gonadal development and digestive tract shrinkage were synchronous after HCG injection. The pituitary – gonad axis plays important role on eel silvering
Use of the sex ratio as a means of resource assessment for the Japanese eel Anguilla japonica: A case study in the Kaoping River, Taiwan
No full text[[abstract]]A negative relationship between the proportion of females and the population density was found when compiling historical data of both wild and cultured Japanese, European, and American eels. Based on the relationship, the population status of the Japanese eel Anguilla japonica was assessed. Japanese eel samples were collected from the lower reaches of the Kaoping River in southwestern Taiwan from 1998 to 2002, and the population density was estimated by mark-recapture experiments in 2001 and 2002. The sex ratio of the eel was skewed towards females, accounting for 81.3%-88.3% in the total samples of yellow and silver eels and for 63.6%-81% in the silver stage eels. The significant female-skewness of the sex ratio validated that the population of Japanese eels in the Kaoping River has declined to a very low level in recent years. The population density of the Japanese eel in the lower reaches of the Kaoping River was approximately 0.01 eeis/m(2) in 2001 and 2002. The decline in the Japanese eel population in the Kaoping River has probably resulted from both overfishing of glass eels in the estuary for aquaculture needs which severely influences recruitment, and degradation of the growth habitat of the yellow eel along the river. The sex ratio therefore is a fast and reliable indicator for eel resource assessment
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