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.
This is a comparative study for understanding the low fish production in the Goh region (Central-Western of Côte d'Ivoire) through the management of the five main fish farms. The study was carry out during 35 days, from August to September 2017. The farmers were all over 45 years old men and sexing fish late. The by-products (rice bran and low flour) were used for feeding on all farms, but only Bahompa 2 farm, makes a supplement with the industrial granulated food. Fish growth parameters have been taken with 200 individuals of Oreochromis niloticus per farm (1000 fish). The main performance indicator such as Daily Weight Gain (DWG), Specific Growth Rate (SGR) and relative condition factor (K) have been calculated for each farm. The best performance of the fish have been recorded on the Bahompa 2 farm (DWG= 1.54 ± 0.47 g/day, SGR = 2.04 ± 0.36%/day and K = 1 ± 0.01. Yopohoué farm follows, with DWG = 1.18 ± 0.31 g/day, SGR = 1.81 ± 0.3%/day, and K = 1 ± 0.01. Bahompa 3 farm were third with DWG= 0.89 ± 0.72 g/day, SGR = 1.15 ± 0.46%/day and K = 0.99 ± 0.04. Bahompa 1 farm, were fourth with DWG = 0.68 ± 0.19 g/day, SGR = 2.02 ± 0.41%/day and K = 1 ± 0.1. Then Sanepa farm were the last with DWG = 1.11 ± 0.18 g/d SGR = 1.21 ± 0.11%/day and K = 1 ± 0.98. The allometric coefficients (b <3) reflect the slow growth of these fish. These low parameters indicate living stress of Oreochromis niloticus fishes during their breeding.
1 ABSTRACT
The phenotypic characterization of four populations of Oreochromis niloticus (Linnaeus, 1758) from the Haut-Sassandra region was carried out using 147 specimens. Among them, 39 were from the natural environment (Sassandra River) and 108 from three fish farms in the town of Daloa. The body weight, sixteen (16) metric characters and fifteen (15) meristic characters recorded on each individual made it possible to analyze the phenotypic variability of the four populations. Twenty-eight (28) on the 31 morphometric characters studied differentiated populations (P <0.001). Based on these 28 characters, Principal Correspondence Analysis (PCA) and Hierarchical Classification Analysis (HCA) grouped the individuals into two groups, a group consisting of Guessabo and PK 12(Kilometer 12 fish farm located at the end of the city of Daloa) specimens and the other group consisting of APDRACI and Quartier Manioc (two fish farms in the city) individuals. Six morphometric characters (PrAL. IOD. LDF. DAL. AFL and SsL) were the most relevant in the discrimination of these two groups. Discriminant factor analysis (DFA) has also classified these populations into two clusters identical to those of the PCA and the HCA. The brood stocks of PK 12 farm is morphologically identical to specimens of the natural environment (Guessabo). The waters of the PK 12 farm have similar characteristics to the natural environment. The PK 12 farm compared to the others (APDRACI and Quartier Manioc) would be better managed.
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