CHAPTER ONE
1.0 INTRODUCTION
1.1 Animal Variation
Variability is the fundamental and basic characteristics of life. Every level of organization of life displays variation in some parameters, in space or time, within and between cells, tissues, organisms, populations and communities. The existence of variations in natural populations of organisms is a necessary condition for evolution. While variability is both a product and foundation of the evolutionary process, biologists are still confronted with the basic problems of explaining the nature, extent and causes of this web of complexity (Reynaldo and Cesar, 2014). Genetic variation is one key factor in the survival of species. Natural populations are perhaps the best gene banks which are critical resources for genetic variation for current and future application in improvement of farmed species of fish (Dunham, 2004). Morphological differentiation is one of the several approaches which have proved useful in studying variability. Morphological data alone, however, is insufficient to explain variability. Molecular biology, biochemical analysis and other methods coupled with morphology are powerful means in understanding variability and evolutionary relationships among and within populations of organisms (Reynaldo and Cesar, 2014).
Among populations, genetic diversity can also be gained when populations that are not normally in contact with another hybridize that is when isolated population experienced migration, gene flow and genetic drift. This can occur when physical barriers are removed such as when fishes are introduced to an area or escape, or when migration patterns changes due to environmental condition. Populations of many species of organisms may respond differently, both morphologically and genetically, to a changed environment. Individuals tend to express different phenotypes (morphological, physiological or behavioural) when surviving in varied environments (Freeman and Herron, 1998). To this end, genetic studies of fish populations play an important role in the sustenance of genetic diversity (Seeb et al., 2007). Genetic markers can provide valuable information about geographic structuring, gene flow and demographic history of populations that can be highly relevant for conservation and management purposes (Maes and Volckaert, 2007).
Water quality tolerance of catfish is diverse due to environmental changes. The warmer the water, the less the dissolved oxygen likewise, the greater the altitude, the less the dissolves oxygen, causing severe cases and death aquatic organisms including catfish. According to F.A.O., (2003), water quality requirement for catfish are as follows; temperature – 26 to 32oC, dissolved oxygen – 3 to 10 mg/l or > 3ppm, pH – 6 to 8, Alkalinity – 50 to 250 mg/l, Ammonia – 0 to 0.03% and Nitrite – 0 to 0.6mg/l. It also reported that for advanced fry, the requirement are as follows; dissolved oxygen – 3-5ppm, temperature – 30oC, ammonia – 0.1 to 1.0ppm, nitrite – 0.5ppm, nitrate – 100ppm, pH – 6 to 9, carbon dioxide – 6 to 15ppm and salinity – 10 to 16ppt.
