The first production of glass eel in captivity: fish reproductive physiology facilitates great progress in aquaculture

Weekly injections of salmon pituitary extracts (SPE) were administered to female Japanese eel, Anguilla japonica at a dose of 20 mg/fish. This induced vitellogenesis and caused oocytes to reach the migratory nucleus stage. Later, a majority of the females that received an injection of SPE at a priming dose, followed 24 h later by 17,20β-dihydroxy-4-pregnen-3-one (DHP), ovulated 15 to 18 h after the final injection. In cultivated males, repeated injections of human chorionic gonadotropin (hCG) at a dose of 1 IU/g BW/week induced spermatogenesis and spermiation. Since potassium ions were revealed to be an essential constituent for the maintenance of motility in the eel spermatozoa, artificial seminal plasma containing KCl was designed as a diluent of milt, and enabled the preservation of milt for several weeks in refrigeration. As a result, artificial fertilization performed immediately after ovulation with pre-diluted and stocked milt consistently resulted in the production of high-quality gametes. Recently, a slurry-type diet made from shark egg yolk has been found to be a suitable feed for captive-bred eel larvae. Although preleptocephalus larvae can be reared with this diet beyond the depletion of their yolk and oil droplet stores, it remains inadequate because larvae reared under this way cannot be raised to the following stage. Therefore, the diet was improved by supplements of krill hydrolysate, soybean peptide, vitamins and minerals. Larvae fed on this new diet have grown to 50 to 60 mm in total length (TL), and have begun to metamorphose into glass eels approximately 250 days after hatching.     

The sex-ratio reversal of the Japanese eel Anguilla japonica in the Kaoping River of Taiwan: The effect of cultured eels and its implication

The sex ratio of wild Japanese eels in the Kaoping River of southwestern Taiwan has been extremely skewed towards females in the recent years. However, the sex ratio skewed towards males after Typhoon Mindulle, July 2, 2004 then recovered to the previous female-dominated status in the following year. To determine why the sex ratio drastically changed, eels captured in the river were examined by both morphologic characteristics and otolith elemental signatures by solution-based inductively coupled plasma mass spectrometry (SB-ICPMS) and laser-ablation ICPMS (LA-ICPMS). Most of the eels collected in the river after the typhoon had a blue-gray colored back, with morphology and sex ratio similar to that of cultured eels, which differed from wild yellow eels which had a green colored back. The chemical signature in otoliths of eels with a blue-gray colored back was similar to that of cultured eels, with significantly lower Sr/Ca ratios but slightly higher Mn/Ca ratios than for wild eels. This confirmed that the reversal in eel sex ratio in the Kaoping River estuary resulted from cultured eels that had escaped from eel farms. Eel farmers estimated that about 30,000 eels escaped during the typhoon, sufficient to reverse the sex ratio of the eels in the river. Furthermore, silver eels caught in the estuary in the winter 2004 were also mostly males. The chemical signature in otoliths of these silver eels was similar to that of escaped cultured eels. Their morphology and mean GSIs, however, were comparable to wild silver eels. Thus, cultured eels that have escaped from eel farms can silver normally in the wild. Consequently, cultured eels may help to balance the sex ratio of the wild eel population and may contribute to the spawning stock of Japanese eel.     

发酵豆粕部分替代鱼粉对日本鳗鲡生长性能和体内矿物元素的影响

在日本鳗鲡（Anguill japonica）饲料中分别添加0、50 g·kg-1、100 g·kg-1、150 g·kg-1和200 g·kg-1的发酵豆粕,相应替代饲料中鱼粉使用量的0、5%、10%、15%和20%,饲养体质量为（37.62±0.16）g日本鳗鲡50 d,研究发酵豆粕对鳗鱼生长性能和体内矿物元素的影响。结果显示：1）随着发酵豆粕替代鱼粉的比例升高,鳗鱼增重率和特定生长率呈先上升后下降的趋势,其中15%替代组增重率和特定生长率高于其他组,但差异不显著（P﹥0.05）,5%替代组饲料系数显著低于其他组（P〈0.05）。从生长性能上看,15%是发酵豆粕替代鳗鱼饲料中鱼粉的最适比例;2）发酵豆粕替代鱼粉后鳗鱼饲料中的钾（K）、铁（Fe）、镁（Mg）等元素质量分数升高,而铝（Al）元素质量分数降低,按变化幅度大小排列Al〉K〉铜（Cu）〉硼（B）〉钙（Ca）〉钠（Na）〉磷（P）〉Fe,但替代组与对照组鳗鱼肌肉中矿物元素K、Ca和P差异不显著（P〉0.05）,而无论是肌肉还是皮肤中矿物元素Cu质分数量均降低（P〈0.05）,因此,发酵豆粕替代鱼粉后应对饲料中矿物元素添加量适当进行调整。