1.1 Background of the Study
Food is a complex organic matter which is rich energy for movement and reproduction, materials for growth and replacement of worn-out tissues and for the welfare or wellbeing of every living organism (FAO, 1992). All fishes need energy which must be obtained from its food sources for growth, movement and reproduction (Anupama, 2000; Orensaye, 2005; Lawal et al, 2008; Esenowo, 2017). Understanding food and feeding habits of fish is useful to all scientist who are concerned with any aspect of fisheries (FAO, 1992). The study of the dietary habits of fishes based of stomach content analysis is widely used in fish biology and ecology to indicate the position of the species within a food web and to provide information on the contribution of different prey item to the diet (Owolasi, 2008; Lawal et al, 2010; Honchanou et al, 2017). It also helps in understanding food consumption, feeding and assimilation rate, catabolism, habitat, segregation (Gomos et al, 2002), defining predator-prey relationships, estimation of trophic level (Bagenal and Tesch, 1978) and in the creation of trophic models as a tool for understanding complex ecosystem (Lopez-Peralta and Arcila, 2002; Asuquo et al, 2013; Ekpo et al, 2014; Esenowo et al, 2017). Fisheries ecologist have conducted studies on fishing ecology to evaluate the dietary composition and the food habit of a fish species in order to provide useful information for fisheries management, aquaculture valorization and habitat protection. The success of fisheries management, species conservation and aquaculture development requires knowledge of the trophic ecology of the target species (Gbaguidi et al, 2016, Esenowo et al, 2017). Based on fish habits, fishes can be classified as herbivores, carnivores, omnivores, parasites, scavengers, detritivoresetc (Lawalet al, 2008). Fishes are sources of food for human (consumption) beings and other animals rich in protein and vitamins especially vitamin a (Retinol) (Alune and Andew, 1996; Osigwe and Obiekezie, 2007; Fayeofori, 2013). Statistics have shown that fish account for more than forty percent of the protein diet of two-thirds of the global population (Eyo, 1992; FAO, 1999). It is unfortunate that the protein requirement of most African countries still grossly outweighs its supply. In Nigeria, less than forty percent of the total protein requirements by the people in MET out of which fish constitutes about 41% (Bernard et al, 2011; Abiaobo and Udo, 2017). The silver catfish, ChrysichthysNigrodigitatus (Lecepede, 1803) commonly known as “inanga” or “IyakItu” by Alborigines of AkwaIbom State (Asuquoet al, 2013) is among the dominant African commercial fishes of high economic value and widely serve as food for human consumption in west Africa (Lawal et al, 2010). This catfish belongs to the genus Chrysichthys, it was split off from the family Bagridae by MO in 1991 along with all of the African Bagrids bar one and is now housed in the Claroteidae family although some authors still group it under the Bagridae. They are in the order Siluriformes, class Actinopterygii, phylum Gnathostomata and kingdom Animalia. Synonyms are Pimelodus Nigrodigitatus, Arius acutivelis, MelanodactylusNigrodigitatus, Chrysichthys acutirastris, Chrysichthys buttkoferi, Chrysichthys furcatus, Chrysichthys ogowensis, Chrysichthys macrops, Chrysichthys coriscanus, Chrysichthys lagoensis and Chrysichthys cameronensis (Winemiller and Leslie, 1992). In its natural habitat, the fish can grow to an asymptomatic length of 50cm total length (TL) and exhibit a sexual dimorphism whore the males when fully grown usually have a broader head which they use to dig out their breeding nest in their native habitat (Asuquoet al, 2013). In general the species show grey/blue silvery colour except for the ventral surface which is white. The fins are greyish-pink, the adipose fin is black and the lips and the barbels pink. Chrysichthys Nigrodigitatus exhibits a pointed snout slightly longer than or equal to the width of the mouth and the pre-maxillary tooth plate width made 20-30% of the head length (Iyabo, 2014). They possess large mouth and eyes and relatively small barbels which usually relates to the habitat where they reside, being clear water where large barbels for feeling for food is not needed, hence the large eyes for hunting prey (Asuquoet al, 2013). Chrysichthys species have been found to be a typical example of fish without strict feeding habit. It is regarded as an omnivore because of its ability to use just any material present in its environment (Royle). Chrysichthys Nigrodigitatus is a prominent number of the Claroteids and occurs abundantly in some AkwaIbom State waters (Imo river (Utaewa), Qua Iboe river (Ibeno) and Cross river (Itu)) in Nigeria and several West African countries. In AkwaIbom State in particular and Nigeria in general, Chrysichthys Nigrodigitatus is a highly valued food fish, source of income for the artisanal fishers and contribute to the internally generated revenue of the state as patronage comes from other states (Asuquo et al, 2013). The estuarine water of Qua Iboe river in Ibeno Local Government Area in AkwaIbom State Nigeria is one of the major hydrographic features in AkwaIbom State. It is characterized by two seasons; dry and wet seasons (Ekpo et al, 2014). The shoreline is characterized by muddy/marshy edges. The channel morphorlogy is characterized by very wide channels and very deep pools. The estuary consists of tidal creeks, small brackish water lagoons and mangrove swamps. The vegetation of the mangrove swamps comprises predominantly the red mangroves (Rhizophora harrisonii, R. mangle and R. racemosa), whites mangroves (Avicenna Africana) and black mangrove (Lagunculariaracemosa) and stands of Nypafruticans, phoenix reclinata and Acrostichumaureum also grow in some places. In Qua Iboe river few or no extensive work has been carried out on food and feeding habit of Chrysichthys Nigrodigitatus. Therefore this research is a contribution to understanding the food and feeding habit of C. nigrodigitatus.
Statement of the Problem
The gut content is a reflection of the water quality, all other factors being constant. The natural habitats offer a great diversity of organisms that are used as food by fish, which differ in sizes (microscopic and macroscopic) and taxonomy groups. The anthropogenic activities going on within Ibeno aquatic ecosystem such as oil exploration and exploitation, fishing activities and other agricultural and industrial activities might cause changes in the availability and abundance of aquatic flora and fauna which serve as food to fishes including C.nigrodigitatus hence this research on the food and feeding habits of C.nigrodigitatus becomes imperative.
Aim and Objectives of the Study
The aim of the study is to investigate the food and feeding habits of Chrysichthys nigrodigitatus in Ibeno Fishing Estuary, Mkpanak. The specific objectives of the study includes to;
Determine the diet composition of Chrysichthys nigrodigitatus in Ibeno Fishing Estuary, Mkpanak
Analyze stomach content based on frequency of occurrence and numerical methods.
Determine whether the fish is herbivore, carnivore or omnivore.
Sufficient research in this regards does not exist, hence prompting this inquiry into the food and feeding habits of Chrysichthysnigrodigitatus in, Qua Iboe River Estuary, Ibeno.
Significance of the Study
Information from the biology and food studies of this species can be used during species selection in fish culture. This is particularly useful in polyculture because proper selection of fishes with different feeding habits will prevent or significantly reduce competition during culture. Information on the biochemical composition and energy levels of the ingested food and its absorption in the alimentary canal provides base line data useful in artificial feed formulation for fish during their culture. For instance, a fish whose natural food is low in protein will likely not require a high protein feed during its culture. Such information can save the farmer a lot of money during feed formulation. Generally, the costs of producing adequate fed for predators is higher because they require a lot of protein in their diet; while the feed of herbivores is cheaper since they require less protein. Catfishes require about 40% protein in their diet for proper growth during culture.