ABSTRACT
Investigations were carried out on the oils and fishmeal of fishes collected from the Onitsha regions of the lower Niger river for possible nutritional and industrial applications. A total of 27 species belonging to 25 different genera were collected. From the results obtained, the highest moisture content was recorded for Electricus membranicus with a value of 88.03% while the least value of 59.93% was recorded for Hypeopisus bebe. Extraction of oil and percentage oil yield analysis showed that high percentage oil yields for the fresh and dry fishes of 8.19 and 22.80 were obtained for Hyperopisus bebe and Schilbe mystus respectively while low values for both the fresh and dry samples of 0.21 and 1.05 respectively were obtained for Tilapia zilli. The difference in means for the percentage oil content between the fresh and dry samples was statistically significant (P<0.05). Based on the percentage oil yield of the fresh samples, they were classified into lean, low, medium and high fat fishes. The lean fishes constituted 33.33%, low fat fishes 40. 70%, medium fat fishes 22.22% while high fat fish constituted 3.70% of the total number of fishes sampled. Good yields of fishmeal for the fresh and dry samples of 27.91% and 94.10% were obtained for Papyrocranus afer and Chrysichthys nigrodigitatus while the lower yields of 10.51% and 56.95% were obtained for Electricus membranicus and Hyperopisus bebe respectively. The difference in means for the percentage yield of fishmeal for the fresh and dry samples was statistically significant (P<0.05). The highest values for the cholesterol content in the oils, fresh and dry fishes were 113.00 mg /g of oil, 587.73 mg /100g of fresh fish and 1880.01mg /100g of dry fish recorded for Heterotis niloticus, Brycinus brevis and Brycinus brevis while the least values were 9.50mg /g of oil, 9.41mg/100g of fresh fish and 48.20mg/100g of dry fish recorded for Labeo senegalensis, Tilapia zilli and Tilapia zilli respectively. The difference in means for cholesterol contents in the fresh and dry fishes was statistically significant (P<0.05). The fatty acid analysis showed that the predominant fatty acids in the oils of the fishes of the lower Niger river were linoleic, palmitic, oleic, linolenic and palmitoleic acids. Stearic, docosahexaenoic, eicosapentaenoic, myrisic and lauric acids were present in moderate amounts while myristoleic, arachidonic, capric and caprylic acids were present in very low levels. The nutritionally important omega-3 fatty acids EPA and DHA were each present in 14 samples but predominantly in Protopterus senegalus, Heterobranchus bidorsalis and Mormyrus macrophthalamus at levels of 6.90, 6.60 and 0.97 g /100g fish oil for EPA while DHA was predominantly found in Synodontis clarias, Tilapia zilli and Chrysichthys nigrodigitatus at levels of 5.45, 2.91 and 2.71 g/100g of fish oil respectively. High values for n-6 and n-3 fatty acids for the fish oils were 59.24% and 42.36% obtained from Brycinus brevis and Polypterus senegalus senegalus while the least values were 10.73% and 4.51% obtained from Polypterus senegalus senegalus and Chrysicththys nigrodigitatus respectively. A high value for percentage C-20 + C -22 n -3 fatty acids for the oils was 6.90, recorded for Polypterus senegalus senegalus while 0.37 and 1.21 were recorded for Synodontis clarias for the fresh and dry fishes respectively. However, low values of 0.07 and 0.01 were obtained for Protopterus annectus and Clarias ebiriensis for the oils and dry fishes respectively. Hydrocynus forskalii, Distichodus rostratus, Citharinus citharus, Parachanna obscura, Tilapia zilli, Dagetichtys lakdoensis, Mormyrops anguilloides and Lates niloticus all had a low value of 0.01 for the fresh fishes. The n-3/n-6 is an expression of the levels of n-3 fatty acids against the levels of n-6 fatty acids. A higher value of 3.95 was obtained for Polypterus senegalus senegalus while a lower value of 0.12 was obtained for Brycinus brevis for the oils, fresh and dry fishes. The expression C-20 + C – 22 n – 3/n -6 is more indicative of the value of fish oils and a good value of 0.64 was obtained for Polypterus senegalus while the least value of 0.002 was recorded for Clarias ebiriensis for the oils, fresh and dry fishes respectively. The n-3/n-6 and the C-20 + C-22n-3/n-6 values obtained for the fishes of the Onitsha regions of the lower Niger river fall within the range of values obtained for the temperate fishes although some temperate fishes have very high values. The study therefore indicates that the oils of some of the fishes of the lower Niger river could be good for the control of cardiovascular diseases and production of nutraceuticals or pharmaceuticals while the fishmeal could serve as raw material for the production of animal feeds.
CHAPTER ONE
1.0 INTRODUCTION AND LITERATURE REVIEW
Fishes belong to three of the seven classes under the subphylum vertebrate which are Agnatha, Chondriclthyes and Osteiclthyes. Consequently, they include the animals commonly called the jawless vertebrates, sharks, rays and bony fishes. Their geographical distribution varies widely and range from thermal springs to cold seas. Fishes are also found in mountain torrents as well as in low land streams and while some fishes dwell on the surface of oceans some others prefer the ocean floors and others are mid water oceanic fishes.
Fishes are widely consumed in various parts of the world and are sold as fresh, frozen, dry, salted and dried, smoked and canned fishes. Consequently, it is a major export and import commodity. The fish is processed into fishmeal and fish oil. The meal is used as a source of protein in the production of animal feeds. The oil is used as industrial raw material for various products some of which are printing inks, protective coatings, plasticizers, oil field chemicals, mold-release agents, lubricants and greases, leather tanning, insecticidal, compounds, soaps, fermentation substrates fatty chemicals, press wood fibre board, mushroom culture and hydrogenated oils. Before 1940 fish oil was considered mainly as a source of vitamin A and D. The oil was just considered as industrial oil and used accordingly.
Recently fish oils have been associated with the reduction of cardiovascular and cerebrovascular diseases (CVD). This is as a result of the epidemiological studies among the Greenland Eskimos and Danes as well as the coastal and inland Japanese which showed that there was a very low incidence of CVD among the Eskimos and the coastal Japanese as a result of fish oil consumption when compared to the Danes and inland Japanese who consumed less fish oil (Dyerberg and Jorgensen ,1982; Tamuro et al, 1993). The farmous 20 years Zutphen study firmly established that regular consumption of fish reduced male death from CVD (Kromhout el al 1985). The CVD lowering properties of fish is attributable to the omega-3 fatty acids which are eicosapentaenoic acid and docosahexaenoic acid (Ackman, 1989; Dyerberg and Schmidt, 1993; Haumann, 1997). Volunteer studies with humans also led to the reduction of blood lipids (Mori et al, 1994). Similar investigation carried out in experimental animals also lower the risks of CVD (Charnock, 1994; Kinoshita et al, 1994).
The direct effects of fish oils on the blood lipids are the reduction of triacylglycerol, total cholesterol, VLDL, LDL (Haris et al, 1993) and lowering of platelet adhesiveness (The Report of the British Nutrition Foundations Task Force,
1993). The eicosapentaenoic acid of fish oil also produce the protalandins 3 series which have potent antiplatelet stickiness effects and also are antithrombotic (Erasmus, 1991).
These health benefits of fish oil developed the market and led to a great rise in the economic value and revenue from fish oils (Ackman, 1989; Opstvedt, 1990). Consequently in 1977 the total world production of fish oil was one million metric tonnes (MMT) but by 1986 this has attained a 60% rise to about 1.7 MMT (Opstvedt,
1990) and a total world sales of 0.96$ billion dollar in 2007 (Josupiet, 2009).
In modest terms it can be said that Nigeria is not participating effectively in this global business. This situation is made worse by the fact that the freshwater fish species of Nigeria is the richest in West Africa with more than 268 presently identified (Olaosebikan and Raji, 1998).
In the developed countries of the world consumers are usually aware of the nutritional compositions of the food they consume because most of the food sources have been analysed for their nutrient contents. This serves as a guide to the choices they make for healthy living. Consequently, a lot of the fishes from these countries have also been analysed and their oil contents, fatty acid profiles and cholesterol contents of the oils among other parameters are known. This information series as a guide on the choices of fish they consume as well as the value placed on them. They are also better informed on the fishes that serve as good sources for the preparation of omega-3 fatty acid concentrates. There is therefore the need for us to investigate the different fishes in our water bodies. The Niger river is the largest fresh water body in Nigeria. The Onitsha market is one of the largest in Nigeria and The Niger river (lower Niger river) flows across this city. It therefore serves as a major outlet and can provide an array of capture fishes of the lower Niger river. Therefore, the
investigation of these fishes will enable us to establish some of the nutrient compositions of some of the fishes consumed in Nigeria.
In this study the different genera of fishes in the Onitsha regions of the lower Niger river will be identified. Some basic processing requirements of industrial importance like moisture and fishmeal compositions will be identified. The oil contents of the fishes will be determined. The fatty acid profiles and cholesterol contents of the fish oils and fishes will also be determined. The fatty acid profile will among others indicate the omega-3 fatty acid contents of the fish oils and fishes. The above information are of industrial nutritional neutraceutical and pharmaceutical importance and will lay some basic foundation to create the necessary value for the development of capture and aquaculture fisheries for domestic and export purposes.
1.2 LITERATURE REVIEW
The phylum chordate is one of the phyla in the animal kingdom. It is divided into the subphyla vertebrates, cephalochordates and urochodates. There are sevenextant classes of the subphylum vertebrata. These are Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia. The last four classes are called tetrapods while the first three classes Agnatha (jawless vertebrates) Chondrichthyes (sharks and rays) and Osteichthyes (bony fishes) are commonly called fishes (Campbell, 1993).
The class Agnatha (jawless vertebrates) includes the sea lampreys and hagfishes and presently there are about 60 species of these jawless vertebrates. The class Chondrichthyes are sharks and related fishes having about 750 extant species with their skeleton made of cartilages. However, sharks and rays are the most wide spread members. Sharks gain buoyancy by storing large amounts of oil in their huge livers, nevertheless they are still more dense than water, so anytime it stops swimming, it sinks. As they swim, water enters the mouth and leaves through the gills making it possible for gaseous exchange to take place. Some sharks, many skates and rays spend reasonable time resting on the bottom of the sea during which they pump water actively over the gills. Sharks are carnivorous, have sharp vision but cannot distinguish colours while their nostrils are for olfaction only and not for breathing. Rays have greatly enlarged pectoral fins which are for propelling them through the water. So they are flattened but their tails are whiplike and bear venomous barbs used for defence in some species. They crush mollusks and crustaceans for food using their jaws. The dogfishes are also among the Chondrichthyes (Vines and Rees, 1982).The class Osteichthyes, also called the bony fishes have about 30,000 species thus representing the most numerous class of vertebrates. They are found in seas and freshwater. Most of the fishes we are conversant with are bony fishes. Unlike cartilaginous fishes bony fishes have their skeleton reinforced by calcium phosphate. Their skins often are covered by scales. Glands in their skins produce mucus secretions which make them slimy thereby reducing drag when they swim. They breathe by drawing water over the gills which are covered by the operculum. Water is drawn to the mouth, through the pharynx and exits between the gills through the movement of the operculum and muscles in the gill chambers thereby making it
possible for bony fishes to breathe when they are stationary. Contrary to sharks, swim bladders are present in most bony fishes. It is an air sac which serves as buoyancy regulator in fish. Exchange of gases between the swim bladder and the blood changes the inflation of the bladder thereby adjusting the density of the fish. Unlike sharks many bony fishes can remain almost motionless thus conserving energy.
The bony fishes have three subclasses. They are the ray-finned fishes (Subclass Actinopterygii), the lobe-finned fishes (Subclass Crossopterygii) and the lungfishes (Subclass Dipnoi) (Campbell, 1993).Almost all the families of fishes we are conversant with are ray-finned fishes of the Subclass Actinopterygii. They include the bass, trout, perch, tuna, herring salmon, sea-run trout among others. Among the Polypterini, only Bichir (Polypterus) of the African rivers exists and it has both lungs and ray-fins (Vines and Rees, 1982). However, many species of genius Polypterus exist (Olaosebikan and Raji, 1998).
In the Subclass Crossopterygii, the lobe-finned fishes only one order the Coelacanthini exists (genius latimeria found in East London). In 1952 off Anjouan Island a different genius 1.5 metres, blue in colour was trapped at a depth of twenty metres 200 miles West of Madagascar called Malanii anjouani. (Vines and Rees, 1982).The Subclass Dipnoi, the lungfishes generally are found in stagnant ponds and swamps. They can gulp air from the surface into lungs connected to the pharynx of the digestive tract. Their present occurrence are in Australia (genius Ceratodus), Africa (genius Protopterus) and South America (genius Lepidosiren).When ponds shrink during the dry season lungfishes have the ability to burrow into the mud and rest. The ability to breathe air at the surface is common to both lungfishes and the lobe-finned fishes because they have opening of the nostril into the buccal cavity. So, most lungfishes and lobe-finned fishes can use their lungs to help the gills in breathing.Generally speaking, fish is any gill bearing aquatic vertebrate (or cranite) animal that lacks limbs with digits such as hagfishes, lampreys, cartilaginous and bony fish. Fish is any non tetrapod cranite (animal with a skull and in most cases a backbone) that has gills all through life and whose limbs when present are in the shape of fins (Wikipedia, 2011). Fish includes hagfishes, sharks, rays, ray-finned fish, coelacanths, and lungfish (Wikipedia, 2011). Consequently aquatic animals like shellfish, cuttlefish, starfish, crayfish, jellyfish, cetaceans like whales and dolphins
are not fish. A typical fish is ectomic with a streamlined body for rapid swimming and extracts oxygen from water with gills or uses accessory breathing organ to breath atmospheric oxygen, has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin and a tail fin, has jaws as well as skin usually covered with scales and lays eggs. The various groups of fishes account for more than half of vertebrate species. Of the 28,000 known extant species, 27,000 are bony fish, 970 sharks, rays and chimeras and about 108 are hagfish and lampreys (Wikipedia, 2011).
Fish suffer from diseases and parasites. They prevent diseases through the skin and scales including the mucus layer secreted by the epidermis which traps and inhibits the growth of microorganisms. When pathogens breach these nonspecific defense systems fish has the ability to develop an inflammatory response which increases the flow of blood to the infected areas and delivers white blood cells to destroy those pathogens. When the body of the fish recognizes a particular pathogen a specific defence will be generated (immune response) (Wikipedia, 2011). Recently vaccines have been used in aquaculture and with ornamental fishes like furunclosis vaccine in farmed salmon and koi herpes virus in koi (Wikipedia, 2011) Some fish use cleaner fish to remove external parasites. These small fish like the Bluestreak cleaner wrasses found in coral reefs in the Indian and Pacific Oceans maintain “cleaning stations” where other fish gather and make some specific movements to attract the attention of the cleaners (Wikipedia, 2011). One major threat to the survival of fish and the fishing business is overfishing. It is a threat to edible fish like cod and tuna. The Pacific sardine Sadinops sagax caerulues fishery collapsed from a peak in 1937 of 800,000 tons to 24,000 tons in 1968 after which the fishery was no longer economically viable. While fishery scientists and conservationists push for stringent protection, the fishery industry is having a different view and government is predisposed to support the fishing industry because it is a key employer of labour (Wikipedia, 2011). Plate 1.1 shows (A) Marcusenius senegaliensis and (B) Alestes baremose sourced from Onitsha regions of lower Niger river.
This material content is developed to serve as a GUIDE for students to conduct academic research
EXTRACTION AND CHARACTERIZATION OF OILS OF THE DIFFERENT GENERA OF FISHES FROM THE FRESHWATER OF LOWER NIGER RIVER>
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