Assessment of morphometric variation, growth performance, disease resistance and nutritional value of clariid catfish hybrid (Clarias macrocephalus Gunther, 1864 x Clarias gariepinus Burchell, 1822)

The present study was carried out to access the morphometric variation and performance of crossbreed of Clarias macrocephalus (♀) and Clarias gariepinus (♂), (hybrid CMxCG) and its parental species; female, CM (C. macrocephalus♀ x C. macrocephalus ♂); male, CG (C. gariepinus♀ x C. gariepinus♂). The first objective was conducted to evaluate the effect of hybridization on the breeding performance, growth and survival of hybrid CMxCG and its parental species as a control for a period of 60 days, with fortnightly sampling. For the purposes, broodstock fishes were induced to spawn by intramuscular injection of Ovaprim hormone at the dose of 0.5 mL kg-1 body weight (female) and 0.25 mL kg-1 body weight (male). The result revealed that hybrid CMxCG achived better in breeding performance than C. macrocephalus in regard to fertilization and hatching rate as well as growth and survival. Percentage of fertilization and hatching rate of hybrid CMxCG were 72.62±2.51% and 64.01±9.17%, respectively, which were higher than in C. macrocephalus which recorded 60.76±0.64 % and 28.14±6.51 %, respectively. As for growth performance, the body weight and total lenght of hybrid CMxCG showed significantly larger and longer (p<0.05) than C. macrocephalus at the end of the study period which resulted in 1.54±0.48 g and 5.81±1.09 cm, respectively for hybrid CMxCG and 0.98±0.28 g and 4.77±0.47 cm for C. macrocephalus. Higher survival rate of 58% which significantly different (p<0.05) was noticed in hybrid CMxCG followed by C. macrocephalus (49%) and C. gariepinus (41%). The second objective of this study employed the morphological variation of hybrid CMxCG and its parental species. A total of 30 morphometric measurements and 5 meristic counts were carried out on each specimen using method from Teugels (1986) and Agnese et al. (1997) with slight modification. For the morphometric characters in this present study, eight new measurements were added with one new measurement in the head and seven new meaasurement in toothplate. The results emphasized that the shape of the occipital process and the shape of the premaxillary as well as vomerine toothplate appears to be highly reliable index of morphological discrimination because it’s showed high phenotypic differentiation among all three fish species. Most of the hybrids also showed intermediate morphological characteristics and exhibits more similarities of phenotypic featured to their paternal species after juvenile stage which might be due to paternal dominating characteristics. The third objective of this study was to evaluate the nutritional composition of hybrid CMxCG, C. gariepinus and C. macrocephalus. Analyses on proximate composition revealed that hybrid CMxCG had the highest protein content (40.07±0.09%) than both parental species (CM: 39.84±0.07%; CG: 38.54± 0.05%). Fatty acid analysis was also done in triplicate consisted of two consecutive steps which were preparations of fatty acid methyl ester (FAME) and gas liquid chromatography. In this study, fatty acids varied between species, demonstrating high polyunsaturated fatty acids (PUFA), EPA, DHA in hybrid CMxCG with the value of 31.41±0.94%, 2.02±0.09 and 2.42±0.40%, respectively. However, no significant difference (p>0.05) was observed in total amino acids (EAA) content of hybrid CMxCG. Apart from that, this study also was conducted to assess the resistance of hybrid CMxCG and its parental species towards bacteria, Aeromonas hydrophila. The PCR primers used for specific detection of A. hydrophila was tested successfully and a desired PCR product of 685 bp was obtained. For aerolysin gene detection, bacteria isolates produced a 309 bp amplicon as expected. In the next phase of the study, fishes were intraperitoneally injected (0.1 mL) with different A. hydrophila concentrations; T0= control (0.85% saline solution); and five serial dilutions (10-9, 10-8, 10-7, 10-6, and 10-5) of A. hydrophila into juveniles of hybrid CMxCG, C. gariepinus and C. macrocephalus. The last objective of this present study revealed that 96 h-LD50 calculated using the Reed and Muench (1938) method was higher in hybrid CMxCG (x106.09 cfu mL-1) than C. macrocephalus (x105.36 cfu mL-1) but lower than C. gariepinus (x106.33 cfu mL-1). Intraperiteonal injection resulted in 100% mortality at the highest concentration of bacteria (109 cfu mL-1). Lesions scores were observed to be more severe in C. macrocephalus particularly in the kidney tubules with significantly higher (p<0.05) mean lesion score as compared to C. gariepinus and hybrid CMxCG. In conclusion, the present study has provided important information on morphometric variation which can be used as quick and cheap method in identifying and distinguishing the parental species and the hybrids especially for field application. Hybrid CMxCG also have showed good performance of important traits which is beneficial for future aquaculture industry in regard to growth and disease resistance. Moreover, hybrid CMxCG revealed better performance of flesh quality content such as protein, PUFA, EPA and DHA, hence, aquaculturing of hybrid can contribute to a better source of protein diet for human being.

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