Mechanisms controlling egg size and number in the rainbow trout, Oncorhynchus mykiss

Tyler, C.R.; Pottinger, T.G.; Santos, E.; Sumpter, J.P.; Price, S-A.; Brooks, S.; Nagler, J.J.. 1996 Mechanisms controlling egg size and number in the rainbow trout, Oncorhynchus mykiss. Biology of Reproduction, 54 (1). 8-15. https://doi.org/10.1095/​biolreprod54.1.8

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Abstract/Summary

Female rainbow trout (Oncorhynchus mykiss) produce a single batch of eggs each year; synchronous growth of oocytes, all of which are ovulated at the same time, occurs in the two ovaries. To examine the regulatory mechanisms controlling egg size and number, virgin female rainbow trout were subjected to unilateral ovariectomy (ULO) during early vitellogenesis, and oocyte recruitment and growth in the remaining ovary were monitored. The study also set out to determine whether the presence of a second population of smaller oocytes in the maturing pool (induced by ULO) affected the timing of ovulation and/or the size of the eggs ovulated. Two months after ULO, there was no difference in the gonadosomatic index between ULO fish and controls. Compensatory ovarian hypertrophy resulted from the recruitment of a second population of primary oocytes into the vitellogenic pool. This population of smaller maturing oocytes in the ULO fish displayed growth rates up to twice those of the population of larger oocytes in the same ovary and of oocytes in controls. The growth rate of the population of larger oocytes in the ULO fish was not altered by the recruitment of a second maturing population. One month after ULO, fish had a lower concentration of plasma estradiol-17β than did controls; subsequently the concentrations of plasma estradiol-17β in the ULO and control groups were similar. After ULO, plasma levels of vitellogenin in the ULO fish did not differ from those in the control group throughout the study. At or close to ovulation, the fecundity of ULO fish was 75-80% that of controls. In the control group, oocytes appeared to reach a certain critical size before they were ovulated, and fish with higher fecundity ovulated later than their less fecund counterparts. ULO did not affect the timing of ovulation, and ULO fish ovulated eggs with a considerably greater size-range than did controls.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1095/​biolreprod54.1.8
UKCEH and CEH Sections/Science Areas:	_ Pre-2000 sections
ISSN:	0006-3363
Additional Information. Not used in RCUK Gateway to Research.:	Click on the Official URL to access full text
Additional Keywords:	rainbow trout, Oncorhynchus mykiss, reproduction, oocyte recruitment, estradiol, fecundity
NORA Subject Terms:	Zoology Biology and Microbiology
Date made live:	28 Jul 2015 10:29 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/510955

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