Determination of the Sexual Maturity of Threadfins Polydactylus quadrifilis (Cuvier, 1829), Galeoides decadactylus (Bloch, 1795) and Pentanemus quinquarius (Linné, 1758) of the Artisanal Marine Fishery of Grand-Lahou (Ivory Coast)

Abstract

Reproduction of the threadfins of the costal shelf of Grand-Lahou was studied with a monthly sampling frequencies range from may 2009 to april 2011. 534 specimens of Polydactylus quadrifilis, composed of 315 males and 219 females and 648 Galeoides decadactylus composed of 420 males and 228 females, then 453 individuals of Pentanemus quinquarius composed of 210 males and 243 females were used.
 The sexual maturity parameters of threadfins fishes indicate a size of first maturity (L50 = 67.5 cm) for females of Polydactylus quadrifilis and (L50 = 55.5 cm) with their males. Concerning the specimens of Pentanemus quinquarius, females present (L50 = 15 cm) and their males (L50 = 14.5 cm). This parameter has identical values ​​with the females of Galeoides decadactylus (L50 = 15.5 cm) and their males (L50 = 15.5 cm). The individuals of Polydactylus quadrifilis and the specimens of Galeoides decadactylus and Pentanemus quinquarius become mature at 1 year of age. The sex ratio determination show that specimens of Polydactylus quadrifilis show a predominance of males during the warm season, from October (73.68%) to March (64.28%) which weakens during the cold season, from May (30%) to July (58%). For Galeoides decadactylus, the sex ratio shows a predominance of males, from August (88%) to March (94.73%). Concerning specimens of Pentanemus quinquarius, the sex ratio is in favor of the females whose lowest value is during the cold season in July (21.74%).
 All threafin species reach sexual maturity from their first year of life with different sex ratios variations.

Spawning, length-growth, mortality and exploitation rate of galeoides decadactylus exploited from the artisanal fisheries of Sierra Leone

“…Further, the present study indicated long-overdue first sexual maturity in both sexes of the assessed stock (Female, L 50% = 50% L max; Male , L 50% = 35%L max ). A similar length at first sexual maturity observed for female specimens in the present study has been revealed for G. decadactylus (L 50% = 18.5 cm [24], but much lower value for both sexes has also been reported (L 50% <16 cm TL: [20,25,26] .…”

“…Results statistically portrayed numerical gender equality in the population of G. decadactylus owing to the insignificant deviation (p>0.05) of the observed sex ratio from the hypothetical ratio of 1:1 in spite of the colossal gap in the female: male sex ratio of 1:1.8. A similarly biased female: male sex ratio has been observed for the study species (F: M, 1:1.8; 1:1.27; 0.46:1) [20,21,22] . Major spawning in G. decadactylus may be occurring in October owing to high GSI relative to increased liver weight (HIS), and the species could be a partial spawner due to its protracted spawning behaviour (August through October).…”

“…Other growth parameters from this study also suggested a slow growth rate (K), earlier age at birth (t 0 <1 year) and death (t max <12) for G. decadactylus in Sierra Leone, compared to other West Africa regions. A slower growth rate [3,27,28,31,32] , similar theoretical age (t 0 = -0.75 and greater longevity t max = 15.8 years [3] , and much lower 't 0 ' [21,31] have been observed in the assessed fish. Slightly higher theoretical age (t = -0.82) and higher longevity (t max = 14.98) of the assessed species from the Ghanaian coast have also been noted [31] .…”