Abstract
Approximately 3 mo before spawning, Pacific herring (Clupea harengus pallasi) were captured and transferred to experimental netpens varying in fish density, cover, and feeding regimes. Fecundity decreased as the fish ripened. Concurrently, ovary weight and egg weight increased and somatic weight decreased. Length-specific fecundities of fed and unfed fish were similar, but the unfed fish had higher weight-specific fecundities, corresponding to a greater loss of somatic tissue during impoundment. Feeding accelerated the rate of maturity, and fed fish spawned earlier with heavier eggs than unfed fish. Relative fecundity (eggs per gram) was highest among the unfed fish. Reduction in preovulatory egg number probably was a consequence of follicular atresia (observed but not quantified here). Age-, length-, and weight-specific fecundity of impounded herring varied within the range observed for naturally maturing populations (1974 and 1980). Fecundity in impounded fish varied no more than observed in nature: there was a greater difference in age-, length-, and weight-specific fecundity between years than there was between experimental treatments. We suggest that reduction in the number of maturing oocytes occurs naturally and reflects a mechanism that allows herring to adjust their egg size and egg number according to energetic resources and environmental conditions.
Published Version
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