GENERAL INTRODUCTION

Transcription

1 GENERAL INTRODUCTION Fish is an important source of protein to humans and other animals fish industry also offers employment opportunities to many people as well as income at house hold and national level (FAO 1996 and Srivastava 1988). Due to the rapid rise in human population, there is tremendous pressure on natural fish resources, which are on the decline (FAO 1996). It is estimated that about 10 million tons of fishes are required annually to meet the present day s demand of fish protein in India against the annual production of only 3.5 million tons (Shukla and Upadhyay, 1998). Fishes encompass the most numerous vertebrate group characterized by an exclusive diversity of feeding habits and food items (Sabu, et al., 2014). Functional morphology of feeding deserves detailed exploration because of its intimate linkage to all aspects of fish evolution and biology. There are few creatures on the earth that have developed such an interesting and unique set of physical characteristic such as fish. Their special adaptations have allowed them to survive in an environment completely different from human.yet despite obstracles in life fish have some unique anatomical adaptations that allow them to flourish. The success on good scientific planning and management of fish species largely depends on knowledge of their biological aspects in which food and feeding habits include a valuable portion. Nutrition of fish is directly related with the amount of fish population (Joadder, 2006). The dietary analysis of fishes indicates the trophic segregation pattern among the members of the fish community in that area (Sabu, et al., 2014). The structure of the digestive system of teleost varies with different factors. Its functions include digestion, nutrient absorption, hormone secretion, immune protection and water and salt transfers for hydro minerals homeostasis (Khojasteh, 2012). Several morphological and physiological adaptations have been evolved in fishes for the digestion of different kind of food found in the gut (Khanna, 1996). An extensive work has been done on gross anatomy and morphology of fishes. Mohsin (1962) described a comparative morphology and histology of alimentary canal in certain group of Indian teleost. 1

2 Kapoor (1957) has done work on the digestive tube of an omnivorous cyprinoid fish Barbus stigma (Cuv. and Val.). Chandy and Georoe (1959) studied alimentary tract of milk fish Chanos in relation to its food and feeding habits. Bahuguna, et al., (2008) worked on gross histomorphology of Schizothorax plagiostomus (Heckel). Recently studies on anatomy of fishes have been carried out by Hassan (2013), Farag. F. M. M, et al., (2014), Upadhyay (2008), Kato and Britz (2011), Ikpegbu, et al., (2012). The gut is a tubular structure it begins at the mouth and ends at the anus. Gut can be subdivided into four topographical regions. The head gut, foregut, midgut, and hindgut (Khojasteh, 2012). The most anterior part, the head guts consist of two components the oral (buccal), gill (brancheal, pharyngeal) cavities. The foregut begins at the posterior edge of the gills and consists of oesophagus, stomach and pylorus. The foregut consists of the oesophagus and an intestine anterior to the opening of the bile duct. The midgut includes the intestine posterior to the pylorus, often with no distinct demarcation posteriorly between it and the hindgut. Number of pyloric caeca pyloric appendages is also present in the midgut. The midgut is always the longest portion of the gut coiled into complicated loops when longer than the visceral cavity. The oesophagus is mostly short, broad, muscular passage way between the mouth and the stomach. Taste buds are usually present along with additional mucus cells. Freshwater fishes have longer esophageal muscles than marine fishes because salt water fish tend to lose water due to osmosis their kidney returns water to the body reverse happens to freshwater fishes, they tend to gain water osmotically. The stomach may be classified into four configuration which include a straight stomach with an enlarge lumen, as in exosa U-shaped stomach with enlarge lumen, a stomach shaped like a Y on its side, the stem of the Y forms a caudally-directed caecum and the absence of stomach. Each fish have a convenient shape of stomach for containing food. The transport of food from stomach into the midgut is controlled by muscular sphincter the pylorus. So the stomach assumes different forms in different fish species. Most of the carnivorous fishes have elongated stomach while omnivorous fishes have sac like stomach. Some fishes contain stomach capable of huge distention and some fishes 2

3 have no stomach instead of stomach they have assesory adaptations for grinding, teeth to crush the food. Intestine of fishes consists of structure similar to those found in terrestrial vertebrates. The primary function of the intestine is the completion of the digestive processes stored in the stomach and the absorption of nutrients (Khojasteh, 2012). Gut length of fishes also differs in size. The carnivorous fishes consume meaty food which gets easily digested than plant material so they have short intestine on the other hand herbivorous fishes consume mostly plant matter, so they have long and sometime coiled intestine. Some species of bony fishes have an intestine with a relatively smooth surface others have longitudinal folds or folds forming a rather complex pattern or network and still others have villi, very small to those found in higher vertebrates (Khojasteh, 2012). Digestive system of fishes consists of mouth, throat and places for the absorption of food materials and compaction of waste products due to the adaptations in diet many differences occurs in the structure of the mouth and the stomach, such type of differences also occurs in the gill rakers, the pharynx, the stomach and in the intestine. Fish ingest food through the mouth and break it down in the oesophagus, food is further digested in the stomach in many food processes in finger shaped pouches called pyloric caeca which secrete digestive enzymes. The intestine completes the process of digestion and nutrient absorption. Food play a vital role in growth and therefore fish migration and abundance of stocks are also related to availability of food (Kurup, 1993). Teleost as an important source of food supply for humans, have successfully adapted themselves to every type of aquatic habitats (Khojasteh, 2012). Various anatomical features confine their feeding types which can be categorized as either herbivorous or carnivorous or omnivorous (Shrestha, et al., 2008). Different fish species living together in confined water body may not have the same feeding habits (Shrestha, et al., 2008). It is also known that the feeding habits changes with different life stages (Kumar, et al., 2009). In general growth of fish is influenced by the quality and quantity of food materials available and consumed so any variation in quality and quantity of food materials will affect the growth rate of fish (Kumar, et al., 2007). Khabade (2015) reported feeding of most fishes in nature may 3

4 presumed to be upon bacteria, desmids, diatoms and other microscopic plankters, both plant and animal and open water pelagic organisms eaten includes algae, protozoan's and microcrustaceans, debris, plant stems and leaves. The quality and quantity variation of natural food materials in a water body are under the influences of several biotic and abiotic factors. These variations could be known by qualitative and quantitative analysis of gut content of fish or by estimating of gastro somatic index (Kumar, et al., 2007). So the seasonal variations also affect the intake of food items in fishes (Shrestha, et al., 2008). According to Alam, et al., (2011) there is considerable variations in food and feeding habits of different fishes depending on the availability of food in the environment. Royce, et al., (1972) reported food and feeding habits of fishes have a great significance in aquaculture practices and also dominant activity of the entire life cycle of fish. Proportion of empty stomach and the amount of ingested materials were significantly influenced by water temperature, turbidity as well as fish hunting behavior and efficiency while the quality and quantity and type of prey were usually of little significance (Ajah, et al., 2006). Many workers have concluded that the number of suitable sized prey in the environment is the main factor involved in food selection (Ajah, et al., 2006). Food selection of fishes may depend on the type of natural food present in the field as well as on the agro climatic conditions therefore the study on feeding behavior strategy becomes important in order to identify the natural feed being ingested by the fish (Awasthi, et al., 2006). According to Khabade (2015) the food of the various fish species varies with life history stages, the kind of food available and change with the season, the food studies may show details of the ecological relationships among organisms. Hynes (1950) reported, the food and feeding habits of fish vary with the time of the day, season and size of the fish, various ecological factors and different substances present in the water body. Investigation on the food and feeding habits of fish species is of high interest to both the aquaculturist and fish biologist, this is because it contributes to the basis for the development of a successful fisheries management programs on fish capture and culture (Oronsaye, 2009). Hence by studying food and feeding habits one can understand what 4

5 programs should be taken for the development of the water bodies to produce more fishes (Mandol, et al., 2005). The study on the food and feeding habits of cultivable species provide vital clues in developing supplementary feed for fish species (Kumar, et al., 2009). Good nutrition in animal production system is essential to economically produce a healthy, high quality product (Steven Craig, et al., 2009), and fishes especially when reared in high densities require a high quality nutritionally complete balanced diet to grow rapidly and remain healthy (Steven Craig, et al., 2009). Rapid growth of fishes may be linked with the type of food it eats, which means knowledge of natural food of the species is essential so it is a well known fact that the knowledge of fish biology particularly on morphometry, length-weight, condition factors, reproduction, food and feeding habits etc. is of greatest importance (Victor, et al., 2014). Therefore the knowledge of nutritional aspects of culturable species is prerequisite for successful aquaculture practices (Padmakar, et al., 2009). In order to culture and manage the fish on scientific basis knowledge about the various ecological factors which are responsible directly or indirectly for optimum fish production from water body must be improved among the factor food and feeding habits of fishes are the prerequisite to understand the interspecific relationship for efficient management of certain fishes (Mondol, et al., 2005). An understanding of seasonal pattern of feeding ecology in co-existing fishes with strong seasonality is not only important to fishery management but also of therotical interest (Xie, et al., 2000). Analysis of feeding habits and guide structure within this unique ecosystem will enhance the knowledge of fish ecology (Hajisamae, et al., 2003). The food study helps us to identify good or bad environment and indicates the future course of action for proper fishery management (Mandol, et al., 2005). Akpan and Isangedhi (2005) reported that the study on food and feeding habits of fishes contributes to better understanding of the trophic dynamics and food web, which is essential for appropriate fisheries management, it gives an information on seasonal changes of fish because the type and magnitude of food available as well as season it occur plays important role in the history of fish. 5

6 The success of effort to introduce and cultivate new species however will depend on quantitative information about the food and feeding habits, nutritional requirement and tropic ecology of this species therefore a study of food and feeding habits of fishes is very important in any fisheries management programme (Sarkar and Deepak, 2009). According to Pillay (1952) analysis of the stomach content of fish could provide information about the niche of the particular fish in its ecosystem. Kadye (2011) investigated a trophic impact of sharptooth catfish Clarias gariepinus by examining its feeding habits. Loomis, et al., (2011) studied the abundance and stomach content analysis of threadfin shad in lake Mead, Nevada. Food and feeding habits of the Guppy, Poecilia reticulata from drainage canal system in Lagos Southwest Nigeria was studied by Lawal, et al., (2012). Food habits and feeding ecology research are the fundamental tool to understand fish role within their ecosystems since they indicates relationship based on feeding resources and indirectly indicate community energy flux (Yanez-Arancibia and Nugent, 1997) which allows inferring competition and predation effects on community structure (Kerbs, 1999). Daiber and Franklin (1992) studied the food and feeding relationship of the freshwater drum, Aplodinotus grunniens Rafinesque in western Lake Erie. Food and feeding biology of a tropical freshwater catfish Mystus nemurus C and V with the reference to its functional morphology was studied by Khan, et al., (1988). Bran (1975) has described food habits, functional digestive morphology and assimilation efficiency of the rabbit fish Siganus spinus (Pisces, siganidae) on Guam. Magnan, et al., (1994) worked on dietary variations in a freshwater fish species relative contribution of biotic interactions a biotic factors and spatial structure. Nasir (2000) has described food and feeding habits relationship of the fish communities in the inshore water of hor Al Zubair, North-West, Arabian Gulf. Sukran Yalcin, et al., (2000) has determined the stomach content of the catfish Clarius gariepinus Burchell, (1822) in the river Asi (Turkey). Emili Garcia-Berthou (2001) has described the size and depth dependent variation in habitat and diet of the common carp (Cyprinus carpio). Studies on the food and feeding habits of cultivable butterfish Scatophagus argus (Cuv. and Val.) was done by Gandhi (2002). 6

7 Teleost gastrointestinal tract presents a morphology which shows specific variation that correlates with feeding habits, diet, body shape and also environmental conditions (Noaillac and Depeyere, 1974; Kapoor, et al., 1975; Zihler, 1982). It is established that the morphology of the alimentary canal varied considerably in different fishes with different feeding habits (Dasgupta, 1996). The study of digestive system of the teleost fishes is of special interest where it shows a great diversity in form and structure (Hassan, 2013). The length of the intestine varies in different species generally, intestine is short and nearly straight in carnivorous fishes, but long, thin walled and highly coiled in herbivorous species while the omnivorous forms show an intermediate condition (Khanna, 1996). Knowledge of fish alimentary canal morphology is becoming increasingly important in fish digestive physiology and improvement of nutritional protocols (Khojasteh, 2012). Anand, et al., (2012) described that the adaptations of the mouth of fishes to their food are particularly evident in the form of mouth size, shape and structures of the oropharynx, dentition, gill rakers, all these structures are subject to diverse and significant variations and modifications in accordance with the feeding habits of different fishes. The anatomical and histological characteristics of fish intestine are expected to be helpful for understanding the related functional mechanisms and feeding habits which can further helpful for diagnosis some intestinal disease and formulating suitable feeds (Khojasteh, 2012). Structural and functional morphology of the alimentary canal has been interest in the adaptation of teleost (Ikpegbu, et al., 2013). There is usually a direct corelation between the structure of the digestive system and the feeding habits of the fish (Hassan, 2013). The alimentary canal of all teleost is built on the same fundamental plan, but studies undertaken so far have shown that within the fundamental plan there is considerable variation in details depending on the difference in feeding habits (Mercy and Pillai, 1985). Importance of food in the daily life of a fish is reflected in the form of mouth, jaws and dentition, the shape and size of gill rakers etc, therefore the difference in their 7

8 feeding habits (Anand, et al., 2012). The characters of dentition are a clue to the fishes feeding habits and the kind of food it consumes. The buccopharynx of fishes performed two important functions (a) respiration and (b) catching the food and conveying it to oesophagus. Morphological data are also key to understand fish nutrition in ecology and aquaculture and during development as well as mechanism for physiological adaptations to a changing environment (Anand, et al., 2012). In herbivorous, the small mouth is not highly protractible or not at all this is due to the fact that the object which it takes hold on is small and stationary (Geetha, et al., 1990). Absence of teeth on the jaws accounts for the fact that the fish feeds mainly on inactive food such as algae and plant materials for which there is no need for active chasing and chewing (Geetha, et al., 1990). Mouth exhibits a variety of fascinating adaptations for capturing, holding and sorting food, ratcheting it into the oesophagus and otherwise manipulating it to entry into the stomach (Harder, et al., 1975). Anand, et al., (2012) reported that the mouth structures associated in different fish species may be considered as mainly concerned with selection, capture, deglutition and pre digestive preparation of food and the effectiveness of this structure are dependent on modifications in relation to food and feeding habits of the fishes and environmental niches inhibited by them. In fishes, as in other vertebrates, the taste buds are the peripheral sense organs of the gustatory system (Reutter, et al., 2000). Taste buds in fish participate in food identification by detecting distinct chemical substances at short distance (Devitsina, et al., 2010) Taste buds of teleost varied in structure depending on the species examined and even on their location in the body (Sadatfar, et al., 2010). In teleost, taste buds are distributed on the gill-rakers and arches, on appendages such as barbells and fin as well as within the oral cavity, unlike humans, they are not usually found on the tongue (Ostrander, 2000). Linser, et al., (1998), reported the colocation of large numbers of teeth and taste buds in the pharyngeal jaws situated immediately anterior to the oesophagus. Reutter, et al., (1974) gave detailed information about the surface of the three types of taste buds to compare the surface of fish taste buds with the surface of taste buds of higher vertebrates. Fishelson and Delarea (2004) compared the shape, number and 8

9 distribution of taste buds on the lips and in the oropharyngeal cavity in fishes belonging to two families, Blenniidae and Gobbiidae which occupy similar ecological niches. When feeding habits changes, many histological changes occur in various parts of the gut (Khanna, 1996). Structural and functional morphology of the alimentary tract has been interest in the adaptations of teleost (Ikpegbu, et al., 2013). According to Cinar and Senol (2006) there are considerable differences in macroscopic and microscopic features and also functions of alimentary canal among fish species, although it shows some basic structural similarities and the overall morphology is related to different feeding habits including the nature of the food and frequency of food intake as well as taxonomy, body size and shape. Histology provides morphologist a powerful tool that enhances the nature, form and detailed structure of organs (Ikpegbu, et al., 2013). Histology is the study of tissue, groups of cells with similar structure that function together as a unit and it provides a description of an organism on a fundamental level (Slough, 2009). Tissue is made up of cells, it forms organs and form organ system while organ system forms an organisms. The function of tissue, organ, organ system and organisms are indicated by the type of tissue (Slough, 2009). There are four types of tissues, epithelial, connective, muscle and nervous. Epithelial tissue protect, secretes, absorbers, lines hallow organs and also forms glands, connective tissues provide a supportive framework for the body. Muscle tissue allows the body to move. Nervous tissues control all functions of the body (Slough, 2009). The histological structure of the stomach of numerous fish species generally consist of mucosa, submucosa, muscularis and serosa (Haloi, et al., 2013). Results in previous studies have indicated that some small differences of histological structures among fish stomach are related to feeding habits, food, age, body shape and weight (Fugi, et al., 2001), (Khalaf, 2013). Histological studies on the digestive system of fishes have been well documented by number of workers. Mokhtar, et al., (2015) studied on histological, histochemical and ultrastructural study on the fundic region of the stomach of Nile catfish Clarias gariepinus. Banan, et al., (2011) studied histomorphology of the alimentary canal in silver carp (Hypothlmichthys molitrix). 9

10 Salamat, et al., (2011) gave an account on histological aspects of gut associated lymphoid in Acanthopagrus latus. Marija Nazlic, et al., (2014) has carried out work on histology of the digestive system of black scorpionfish (Scorpaena porcus L.). Namulawa, et al., (2011) gave histomorphologial description of the digestive system of Nile perch (L. niloticus). The present work deals with studies on annual food composition, seasonal variation in food of two teleost fishes Catla catla and Labeo rohita on the basis of their morphological features and gut contents. Attempts have been also made to investigate the relationship between feeding habits and the type of teeth, histological changes in the gut. 10