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The breeding cycle of Scylla serrata (Forskål, 1755) at Ramisi River estuary, Kenya
Onyango, S. D. (2002). The breeding cycle of Scylla serrata (Forskål, 1755) at Ramisi River estuary, Kenya. Wetlands Ecol. Manag. 10: 257-263
In: Wetlands Ecology and Management. Springer: Den Haag; Dordrecht; Hingham, MA; Amsterdam. ISSN 0923-4861; e-ISSN 1572-9834
Peer reviewed article  
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Trefwoord
    Scylla serrata (Forskål, 1775) [WoRMS]
Author keywords
    breeding cycle, madema, ovigerous, Ramisi estuary
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  • Onyango, S. D.
Abstract
    The mud crab Scylla serrate was collected from Ramisi river estuary for a period of 14 months (January 1990– February 1991) using madema traps. For each crab the carapace width (mm), sex and weight were noted, and the number of ovigerous female crabs was recorded. Both ovigerous and non-ovigerous females were dissected in order to observe of the maturity stages of ovaries. The ovarian maturity stages were described as stage zero – virgin/resting, stage one – developing, stage two – well developed and stage three– ripe. The most abundant was stage two throughout the study period. The smallest ovigerous crab had a carapace width of 139 mm. A test of homogeneity of the binomial distribution of the sex ratio showed homoscedasticity (?2 = 14.615; d.f. = 13; p > 0.05) and the overall sex ratio did not differ from 1:1 (? 2 = 0.776; d.f. = 1; p > 0.05). The variance test of homogeneity of the binomial distribution of sex in relation to size showed a very significant heterogeneity (?2 = 32.83; d.f. = 9; p < 0.05). There was no significant difference when the overall mean sizes for males and females were compared using t-test (t = 4.26; d.f. = 18;p <0.001). The relatively high numbers of females with stage two ovaries indicated that spawning took place throughout the year with a possible peak in the second half of the year.
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