Thirty-nine morphometric and five meristic comparisons were carried out on 12-month-old interspecific and intergeneric hybrids of the African clariid catfishes Heterobranchus longifilis, Clarias gariepinus and Clarias anguillaris from experimental earthen ponds in Nigeria. Canonical discriminant analysis accounted for 89.4% of the variations, with eigenvalues of 151.69 and 9.06, respectively, the highest loading in the two axes coming from only 12 variables. A re-analysis based on those 12 variables revealed four major groups among the nine genetic combinations from a plot of axes 1 and 2, which accounted for 95.2% of the variations. The Mahalanobis square distance (D 2 ) between the offspring of the various mating combinations also revealed the varying levels of relationship between them based on their morphometric and meristic characters. The interspecific hybrids showed some level of heterosis only in the inheritance of the length of the frontal fontanelles compared to that of the putative Clarias species. The study shows the level of similarities in many of the morphometric and merisitic features, especially among the hybrids, and the distinguishing features that can be used to identify the hybrids from their putative parents.
The study evaluated the genetic signatures of the fishes from the two populations and compared the pattern of differentiation of the two populations with a view to separating the species from the different populations into possible sub-species. Forty (40) specimens were collected from River Niger (Lokoja) and Asejire Resevoir. The DNA of the twenty (20) specimens from each population extracted from the muscle tissue using phenol-chloroform extraction (PCE) method was subjected to microsatellite DNA analysis. Seven (7) microsatellite markers (Cga01, Cga02, Cga03, Cga05, Cga06, Cga09 and Cga10) were used in the analysis. Microsatellite DNA analysis of the two populations revealed significant differentiation between the two populations as shown by the high values of heterozygosity, low level of inbreeding and non-conformance to Hardy-Weinberg’s equilibrium. It is concluded from the study that microsatellite analysis showed a high potentiality for separation of the populations.
The anesthetic effects of clove (Eugenia aromaticum) seed extract on Clarias gariepinus fingerlings were investigated under semi-arid conditions. Various concentrations of the clove seed extract at 25.0, 50.0, 75.0, 100.0, 125.0 and 150.0mg per liter of water were used for the experiment. Each concentration was tested on a group of 10 Clarias gariepinus fingerlings (24.13 25.30g in weight and 5.97 7.00 cm in length) in glass aquariums. There was a decrease in induction time as the concentration of the clove seed extract increased. Fingerlings treated with 150mg/l of the extract produced the shortest induction time (2.28±0.15 minutes), followed by fish treated with 100 and 125mg/l (3.31±0.55 and 3.07±0.07 minutes, respectively). The longest induction time (10.60±0.98, 7.52±0.25 and 5.96±1.17 minutes) was observed in fingerlings sedated with 50, 25 and 75mg/l, respectively. Recovery was significantly faster (2-3.92 minutes) in fish treated with lower dosages (25 to 125mg/l) of the clove seed extract. Mortality rates after 24 hours of recovery were higher (4.79±0.25 and 3.10±0.54%) in fish anesthetized with higher (150 and 125mg/l) concentrations of the clove seed extract, respectively.
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