Reproductive parameters of the chub mackerel Scomber japonicus estimated from human chorionic gonadotropin-induced final oocyte maturation and ovulation in captivity

Abstract

Final oocyte maturation and ovulation of captive chub mackerel Scomber japonicus with fully yolk-accumulated oocytes were induced by a single injection of human chorionic gonadotropin. Reproductive parameters, including spawning frequency and batch fecundity, which are required to estimate spawning biomass in pelagic fish by the daily egg production method, were analyzed. Germinal vesicle migration (GVM) occurred at 18-24 h post-injection, and the hydration and ovulation of oocytes were completed at 30 and 36 h post-injection, respectively. The results of the maturation process suggest that fish with GVM-stage ovaries captured in the daytime from the field are capable of spawning on the night following their capture. The oocytes used in the oocyte sizefrequency distribution method for batch fecundity estimates should be at late GVM and more advanced stages. The results of sequential artificial insemination showed that the quality of ovulated eggs held in the ovarian lumen rapidly deteriorated as time progressed after ovulation. This indicates that the fertilization window for the ovulated eggs of chub mackerel lasts only a few hours, and spawning behavior should be performed within a few hours after ovulation in the wild population.KEY WORDS: batch fecundity, chub mackerel, fertilization rate, final oocyte maturation, human chorionic gonadotropin, ovulation.

Spawning frequency of the Tsushima Current subpopulation of chub mackerel Scomber japonicus off Kyushu, Japan

“…The estimation of S relies on the prevalence of females within a random subset of the target population who are imminent spawners, have hydrated oocytes in their ovaries, or are recent spawners with POFs. Experiments in captivity [7,8] have shown that the spawning fraction of chub mackerel has a clear daily reproductive rhythm, and sampling for fish with GVBD-and hydration-stage oocytes should be constrained within a short period between daytime and evening. Therefore, hydration methods could not have been used in our study because fishing is performed between midnight and daybreak.…”

“…Nearly 120 fish (278-326 mm in fork length, FL) were transferred to the Fishery Research Laboratory of Kyushu University on 21 May 2001. On the following day, after anesthetization with 100 mg/l 2-phenoxyethanol, 60 female fish with yolk-accumulated oocytes 600-650 lm in diameter were selected via ovarian biopsy as described previously [7]. Additionally, these fish were injected intramuscularly with human chorionic gonadotropin (hCG, 500 IU/kg BW, ASKA Pharmaceutical Co., Tokyo, Japan) at 14:00.…”

“…We recently developed an experimental system using chub mackerel in which the final oocyte maturation (FOM) and ovulation in captivity can be controlled and induced at any time for a period of 3 months during the spawning season [7,8]. Using this system, it is possible to obtain a series of ovary samples at regular intervals from the time of ovulation.…”

“…Thus, the acquisition of age-determined POFs and accurate information outlining the time course of oocyte maturation and ovulation allows the more accurate prediction and determination of the reproductive state of individual females in wild spawning stock. Our objective was to investigate the S of the spawning stock of the Tsushima Current subpopulation based on our previous findings [7,8] for the reproductive state of chub mackerel.…”

Changes in the expression of pituitary gonadotropin subunits during reproductive cycle of multiple spawning female chub mackerel Scomber japonicus

“…From late April to May 2009, four groups of chub mackerel were treated once with GnRHa, respectively. Before the treatment, suitable chub mackerel consisted of spermiating males and females that possessed oocytes greater than 600 lm were selected according to Shiraishi et al (2005). GnRHa injections were prepared by mixing the des Gly 10 -D-[Ala 6 ] LHRH ethylamide (SigmaAldrich) into molten coconuts oil according to the method of Scott et al (1999).…”