ABSTRACT
This research work was carried out to examine the effect of cold and warm shock on hybridized fish order of Siluriformes (Heterobranchus bidorsalis and Clarias gariepinus) in indoor tanks crossing of two different species is a process called hybridization, with the offspring known as the hybrids. The length of the cold shock, warm shock and even the diploid fish ranges from 0.7 to 3.6cm, 0.6 to 3.5 cm and 0.6 to 2.7m while their weight varies from 0.008 to 0.226g, 0.008 to 0.242g and 0.009 to 0.140g after 6 weeks of culture. The hatchability rate for the triploid fish was low. The feed used in raising the hatchlings for the first two weeks were mostly live feed daphnia which encourage growth and are preferred by the fish. This study has shown that bigger Heteroclarias was produced when triploid cold shock than warm shock and diploid. Thus this research has provided information that will enhance the production of bigger fish in aquaculture.
CHAPTER ONE
1.0 Introduction
Aquaculture in Nigeria is in the developing stage, because it has not been able to meet demand and supple of the ever-increasing human population (Ojutiku, 2008).The development of improved fish seed stocks that can contribute to increased fish production and at the same time ensuring protection of biodiversity and the environment is seen as one of the key solutions to securing future food requirement of the growing world population (Lincoln,1980).Genetics and the successful application of breeding programs in crops and livestock have provided the impetus for the governments it has been acknowledged as the most efficient means of providing protein rich food, income generation and employment opportunities for the populace. (Ojutiku 2008) noted the interest in fish culture is growing very rapidly in Nigeria but the scarcity of fingerlings of widely acceptable species of catfish such as Heterobranchus species (Val. 1840) and Clarias species tend to constitute a major constraint to the rapid development of fish farming in Nigeria. He also mentioned that economically productive aquaculture, is heavily dependent on adequate supply of fish stock to ponds and other culture systems.
One of the methods of improving growth performance of aquaculture species is through biotechnology. This could be through hybridization, genetic engineering and chromosome manipulation. The quest to obtain fast growing species to meet the high demand of fish consumers in the populace has lead fish farmers, to manipulate chromosome of various indigenous culturable fish species(Eyo et al; 2003). Chromosome manipulation is the alteration of chromosome numbers to produce polyploids such as triploid and tetraploid (Lawson and Ishola, 2010). Polyploidy is an occurrence in which gamete and somatic cells possess haploid number of chromosomes. Forms of having 3n chromosomes are triploids; 4n, tetarploids; 5n, pentaploids. The techniques that are used to alter the chromosome number are cold, heat, pressure and chemical shocks. This alteration in chromosome number is often associated with advantageous features such as increased size, hardiness, and resistance to disease (Lawson and Ishola, 2010). Besides, the basic goal governing the technology is to produce sterile fish in order to prevent gamete formation, to produce fast growing fish, to improve carcass quality and to utilize exotic species both in fish farming and fisheries management (Lawson and Ishola. 2010).
Mass production of fry, fingerlings and adult of Clarias gariepinus and Heterobranchus bidorsalis through hypophysation, gynogenesis. Hybridization, and polypoidy had been carried out by many scientist among who are (Gheyas et al; 2001; Herbst, 2002; Eyo et al; 2003, Lawson and Ishola, 2010 and Nwachi, 2012).
In fishes, triploidy and tetarploidy may be currently obtained by shocking newly fertilized eggs shortly after fertilization. Fish eggs do not extrude the second polar body until they are fertilized, because of this, if a newly fertilized egg is shocked, the shock prevents the second polar body from leaving the egg; consequently the fertilized egg will contain three haploid nuclei; one from the egg, one from the sperm, and one from the second polar body (Dunham et al; 2003). These three haploid nuclei will fuse to from a triploid zygote nucleus, which creates a triploid, while four haploid nuclei fuse to form a tetraploid zygote.
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