Abstract
Utilising histological preparations of ovaries from Engraulis ringens females collected in two contrasting spawning habitats along the Chilean coast, we assess the variability in oocyte size and batch fecundity during the peak spawning seasons in three years. The effects of female size (length and weight), batch fecundity and mean sea surface temperature on oocyte size were also examined. Results showed larger oocytes and lower batch fecundity in females from the southern area. Oocyte volume differences persisted inter-annually and were not explained by differences in female sizes. Since ovary weight was similar between areas, the cost of producing larger oocytes in the south population seems to be a fecundity reduction. The latitudinal variations in oocyte number and size seem to be determined by the predominant environmental conditions in each habitat. Hence, female E. ringens seem to adapt their reproductive tactics by producing eggs sizes and quantities that favour survival of their offspring under the environmental conditions in which they are to develop.
Highlights
Egg size is a key factor in fish reproductive strategies and its variability is modulated by the trade-off between offspring quantity and quality (Fleming and Gross, 1990)
SUMMARY: Utilising histological preparations of ovaries from Engraulis ringens females collected in two contrasting spawning habitats along the Chilean coast, we assess the variability in oocyte size and batch fecundity during the peak spawning seasons in three years
Female E. ringens seem to adapt their reproductive tactics by producing eggs sizes and quantities that favour survival of their offspring under the environmental conditions in which they are to develop
Summary
Egg size is a key factor in fish reproductive strategies and its variability is modulated by the trade-off between offspring quantity and quality (Fleming and Gross, 1990). A latitudinal trend in egg size has been observed in natural populations, which are distributed over a wide geographic range (De Ciechomski, 60 E.M. Leal et al.1973; Funamoto and Aoki, 2002; Llanos-Rivera and Castro, 2004). Hypotheses proposed to explain this variability include environmental factors such as temperature, oxygen and food availability (Tanasichuk and Ware, 1987; Beacham and Murray, 1993), and biological factors such as size and endocrine state of the female during oocyte growth in the ovary (Hay and Brett, 1988; Ojanguren et al, 1996; Laine and Rajasilta, 1999). Separated by over 15 degrees of latitude, these spawning habitats show strong environmental differences
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