LENGTH-WEIGHT RELATIONSHIP, CONDITION FACTOR AND GROWTH OF NILE TILAPIA
1.1 BACKGROUND OF STUDY
Fish were the first vertebrate animals to evolve and have since given rise to all the vertebrate animals found in water and on land. Fossils of fish have been dated back to the Cambrian period around 530 million years ago during a time when the diversity on Earth was going through a massive explosion. Currently, there are more than 30,000 species found around the world with the largest diversity found in coral reefs in the world’s tropical regions.
Tilapia is a large genus in the cichlid family (Cichlidae) comprising of 1,524 species (Eli, 2005). It inhabits a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. According to Fessehaye et al. (2006), Tilapia is the fifth most important fish in fish farming, with production reaching 1,505,804 metric tons in the year 2000. In 2000 to 2010, Tilapia production increased from 1.27 million metric tons to 3.4 million metric tons. Because of their large size, rapid growth, and palatability, tilapia cichlids are the focus of major farming efforts and research, specifically various species of Oreochromis, Sarotherodon, and Tilapia, collectively known as tilapias.
Tilapia has wide geographical distribution in a lot of natural or artificial water reservoirs in many countries especially those having tropical climates. However, most of the world’s farmed fish production come from developing countries (FAO, 2006; Gil, 2007).The major producing country was China (over 50 percent) followed by Thailand, Philippines, Indonesia, Egypt,
Taiwan, Brazil, Colombia and Malaysia. Other countries with notable production were the USA,
Israel, Cuba, Mexico, Costa Rica, Venezuela and Nigeria (Roderick, 2001). According to Fagbenro et al., 2010, Nigeria is the second largest producer of farm-raised tilapias in Africa, after Egypt. Tilapias are widely cultivated in ponds, reservoirs and cages in Nigeria (Fagbenro et al., 2004) and are suited to low-technology farming systems because of their fast growth rate, efficient use of natural aquatic foods, propensity to consume a variety of supplementary feeds, omnivorous food habits, resistance to disease and handling, ease of reproduction in captivity, and tolerance to wide ranges of environmental conditions (Fagbenro, 1987). Tilapia is also identified under a number of different generic names; it can be called “carpe” in West Africa, “St. Peter’s Fish in Israel, “bream” in Southern Africa, “mojarra” in Latin America.
Nile tilapia (Oreochromis niloticus) is an important fish in the ecology of tropical and sub-tropical region including Nigeria and of great commercial importance in the fisheries in many African lakes (Britton and Harper, 2008). It is also the most popular species of the bony fish for aquaculture in Africa (Abdel et al., 2007). This is attributed to many positive qualities including tolerance to poor water quality, wide range of food, and plasticity in growth, firm flesh and good taste (Fryer and Iles, 1972).
Brief History of Tilapia
Tilapia was a symbol of rebirth in Egyptian art, and was in addition associated with Hathor. It was also said to accompany and protect the sun god on his daily journey across the sky. Tilapia painted on tomb walls, reminds us of spell 15 of the Book of the Dead by which the deceased hopes to take his place in the sun boat: “You see the tilapia in its [true] form at the turquoise pool”, and “I behold the tilapia in its [true] nature guiding the speedy boat in its waters.”
Tilapia were one of the three main types of fish caught in Talmudic times from the Sea of Galilee, specifically the Galilean comb (Sarotherodon galilaeus). Today, in Modern Hebrew, the fish species is called amnoon (suggested derivative: am “mother” + noon “fish”). In English, it is sometimes known by the name “St. Peter’s fish”, which comes from the story in the Gospel of Matthew about the apostle Peter catching a fish that carried a coin in its mouth, though the passage does not name the fish. While the name also applies to Zeus faber, a marine fish not found in the area, a few tilapia species (Sarotherodon galilaeus, Oreochromis aureus , Coptodon zillii and Tristramella) are found in the Sea of Galilee, where the author of the Gospel of Matthew recounts the event took place. These species have been the target of small-scale artisanal fisheries in the area for thousands of years.
The common name ’tilapia’ is based on the name of the cichlid genus Tilapia, which is itself a latinization of tilapia, the Tswana word for “fish”. Scottish zoologist Andrew Smith named the genus in 1840. Tilapia is the official fish of the state of India.
Taxonomy and Nomenclature
Tilapia is the generic name of a group of cichlids endemic to Africa. The group consists of three aquaculturally important genera Oreochromis, Sarotherodon and Tilapia. Several characteristics distinguish these three genera, but possibly the most critical relates to reproductive behaviour. All tilapia species are nest builders; fertilized eggs are guarded in the nest by a brood parent. Species of both Sarotherodon and Oreochromis are mouth brooders; eggs are fertilized in the nest but parents immediately pick up the eggs in their mouths and hold them through incubation and for several days after hatching. In Tilapia species only females practice mouth brooding, while in Sarotherodon species either the male or both male and female are mouth brooders.
During the last half century fish farmers throughout the tropical and semi-tropical world have begun farming tilapia. Today, all commercially important tilapia outside of Africa belong to the genus Oreochromis, and more than 90 percent of all commercially farmed tilapia outside of Africa are Nile tilapia. Less commonly farmed species are Blue tilapia (O. aureus), Mozambique tilapia (O. Mossambicus) and the Zanzibar tilapia (O. urolepis hornorum). The scientific names of tilapia species have been revised a lot in the last 30 years, creating some confusion.
Tilapia is a common name that is now applied to several genera and species of fish that were formerly classified in the genus Tilapia, in the Family Cichlidae. In the reclassification scheme developed by Trewavas (1983) the several hundred species of Tilapia were split into three genera, Oreochromis, Sarotherodon and some remained as Tilapia.
The preferred scientific name is Tilapia zilli, the preferred English common name is Cichlid while the local common name for tilapia in Hausa language which is the main spoken language in Wudil and Kano State at large is “Karfasa”.
Below shows the taxonomic tree of Tilapia zilli
Tilapia typically have laterally compressed, deep bodies. Like other cichlids, their lower pharyngeal bones are fused into a single tooth-bearing structure. A complex set of muscles allows the upper and lower pharyngeal bones to be used as a second set of jaws for processing food (cf. morays ), allowing a division of labor between the “true jaws” (mandibles ) and the ” pharyngeal jaws “. This means they are efficient feeders that can capture and process a wide variety of food items. Their mouths are protrusible, usually bordered with wide and often swollen lips. The jaws have conical teeth. Typically, tilapia have a long dorsal fin, and a lateral line which often breaks towards the end of the dorsal fin, and starts again two or three rows of scales below. Some Nile tilapia can grow as long as 2.0 ft.
Other than their temperature sensitivity, tilapias exist in or can adapt to a very wide range of conditions. An extreme example is the Salton Sea, where tilapias introduced when the water was merely brackish now live in salt concentrations so high that other marine fish cannot survive.
Tilapia are also known to be a mouth-brooding species, which means they carry the fertilized eggs and young fish in their mouths for several days after the yolk sac is absorbed.
Tilapia are shaped much like sunfish or crappie but can be easily identified by an interrupted lateral line characteristic of the Cichlid family of fishes. They are laterally compressed and deep-bodied with long dorsal fins. The forward portion of the dorsal fin is heavily spined. Spines are also found in the pelvis and anal fins. There are usually wide vertical bars down the sides of fry, fingerlings, and sometimes adults.
In all Tilapia species, the male excavates a nest in the pond bottom (generally in water shallower than 3 feet) and mates with several females. After a short mating ritual the female spawns in the nest (about two to four eggs per gram of brood female), the male fertilizes the eggs, and she then holds and incubates the eggs in her buccal cavity until they hatch. Fry remain in the mouth of the through yolk sac absorption and often seek refuge in her mouth for several days after they begin to feed.
Sexual maturity in tilapia is a function of age, size and environmental conditions. The Mozambique tilapia reaches sexual maturity at a smaller size and younger age than the Nile and Blue tilapias. Tilapia populations in large lakes mature at a later age and larger size than the same species raised in small farm ponds. For example, the Nile tilapia matures at about 10 to 12 months and 3/4 to 1 pound (350 to 500 grams) in several East African lakes. Under good growth conditions this same species will reach sexual maturity in farm ponds at an age of 5 to 6 months and 5 to 7 ounces (150 to 200 grams). When growth is slow, sexual maturity in Nile tilapia is delayed a month or two but stunted fish may spawn at a weight of less than 1 ounce (20 grams). Under good growing conditions in ponds, the Mozambique tilapia may reach sexual maturity in as little as 3 months of age, when they seldom weigh more than 2 to 4 ounces (60 to 100 grams). In poorly fertilized ponds sexually mature Mozambique tilapia may be as small as 1/2 ounce (15 grams).
Fish farming strategies that prevent overcrowding and stunting include: 1) cage farming where eggs fall through the mesh to the pond bottom before the female can collect them for brooding; 2) polyculture with a predator fish, such as fingerling largemouth bass, at 400 per acre; and 3) culture of only males (monosex). All-male culture is desirable in ponds not only to prevent overpopulation and stunting but as fast as females. Methods of obtaining predominately male fish include: 1) manually separating the sexes based on visual examination of the genital papilla of juvenile fish ( hand-sexing); 2) hybridizing between two selected species that produce all-male offspring (for example, Nile or Mozambique females crossed with Blue or Zanzibar males); 3) feeding a male hormone-treated feed to newly hatched fry for 3 to 4 weeks to produce reproductively functional males (sex reversal); or 4) YY male technology (currently under development and not yet a commercial option).
The sex of a 1-ounce (25-gram) tilapia fingerling can be determined by examining the genital papilla located immediately behind the anus. In males the genital papilla has only one opening (the urinary pore of the ureter) through which both milt and urine pass. In females the eggs exit through a separate oviduct and only urine passes through the urinary pore. Placing a drop of dye (methylene blue or food coloring) on the genital region helps to highlight the papilla and its openings.
FEEDING BEHAVIOR AND NUTRITION REQUIREMENTS
Tilapia ingest a wide variety of natural food organisms, including plankton, some aquatic macro aquatic invertebrates, larval fish, detritus, and decomposing organic matter. With heavy supplemental feeding, natural food organisms typically account for 30 to 50 percent of tilapia growth. (In supplementally fed channel catfish only 5 to 10 percent of growth can be traced to ingestion of natural food organisms.) Tilapias are often considered filter feeders because they can efficiently harvest plankton from the water. However, tilapias do not physically filter the water through gill rakers as efficiently as true filter feeders such as gizzard shad and silver carp. The gills of tilapia secrete a mucous that traps plankton. The plankton-rich mucous, or bolus, is then swallowed. Digestion and assimilation of plant material occurs along the length of the intestine (usually at least six times the total length of the fish). The Mozambique tilapia is less efficient than the Nile or Blue tilapia at harvesting planktonic algae.
Two mechanisms help tilapia digest filamentous and planktonic algae and succulent higher plants: 1) physical grinding of plant tissues between two pharyngeal plates of fine teeth; and 2) a stomach pH below 2, which ruptures the cell walls of algae and bacteria. The commonly cultured tilapias digest 30 to 60 percent of the protein in algae; blue-green algae is digested more efficiently than green algae.
When feeding, tilapias do not disturb the pond bottom as aggressively as common carp. However, they effectively browse on live benthic invertebrates and bacteria-laden detritus. Tilapias also feed on midwater invertebrates. They are not generally considered piscivorous, but juveniles do consume larval fish. In general, tilapias use natural food so efficiently that crops of more than 2,700 pounds of fish per acre (3,000 kg/ha) can be sustained in well-fertilized ponds without supplemental feed. The nutritional value of the natural food supply in ponds is important, even for commercial operations that feed fish intensively.
In heavily fed ponds with little or no water exchange, natural food organisms may provide one-third or more of total nutrients for growth. In general, tilapia digest animal protein in feeds with an efficiency similar to that of channel catfish, but are more efficient in the digestion of plant protein, especially more fibrous materials.
Tilapia require the same ten essential amino acids as other warm water fish, and, as far as has been investigated, the requirements for each amino acid are similar to those of other fish. Protein requirements for maximum growth are a function of protein quality and fish size and have been reported as high as 50 percent of the diet for small fingerlings. However, in commercial food fish ponds the crude protein content of feeds is usually 26 to 30 percent, one-tenth or less of which is of animal origin. The protein content and proportion of animal protein may be slightly higher in recirculating and flow-through systems.
The digestible energy requirements for economically optimum growth are similar to those for catfish and have been estimated at 8.2 to 9.4 kcal DE (digestible energy) per gram of dietary protein. Tilapia may have a dietary requirement for fatty acids of the linoleic (n-6) family. Tilapia appear to have similar vitamin requirements as other warm water fish species. Vitamin and mineral premixes similar to those added to catfish diets are usually incorporated in commercial tilapia feeds. The feeding behavior of tilapia allows them to use a mash (unpelleted feeds) more efficiently than do catfish or trout, but most commercial tilapia feeds are pelletized to reduce nutrient loss. In the absence of feeds specifically prepared for tilapia, a commercial catfish feed with a crude protein content of 28 to 32 percent is appropriate in the United States.
Tilapia are more tolerant than most commonly farmed freshwater fish to high salinity, high water temperature, low dissolved oxygen, and high ammonia concentrations.
All tilapia are tolerant to brackish water. The Nile tilapia is the least saline tolerant of the commercially important species, but grows well at salinities up to 15 ppt. The Blue tilapia grows well in brackish water up to 20 ppt salinity, and the Mozambique tilapia grows well at salinities near or at full strength seawater. Therefore, the Mozambique tilapia and some mossambicus derived red tilapia are preferred for saltwater culture.
Some lines of the Mozambique tilapia reportedly have spawned in full strength seawater, but its reproductive performance begins to decline at salinities above 10 to 15 ppt. The Blue and Nile tilapias can reproduce in salinities up to 10 to 15 ppt, but perform better at salinities below 5 ppt. Fry numbers decline substantially at 10 ppt salinity.
The intolerance of tilapia to low temperatures is a serious constraint for commercial culture in temperate regions. The lower lethal temperature for most species is 50 to 52o F for a few days, but the Blue tilapia tolerates temperatures to about 48o F.
Tilapia generally stop feeding when water temperature falls below 63o F. Disease-induced mortality after handling seriously constrains sampling, harvest and transport below 65o F. Reproduction is best at water temperatures higher than 80o F and does not occur below 68o F. In subtropical regions with a cool season, the number of fry produced will decrease when daily water temperature averages less than 75o F. After 16- to 20day spawning cycles with 1/2- pound Nile tilapia, fry recovery was about 600 fry per female brooder at a water temperature of 82o F, but only 250 fry per female at 75o F.
Optimal water temperature for tilapia growth is about 85 to 88o F. Growth at this optimal temperature is typically three times greater than at 72o F.
Dissolved oxygen concentration
Tilapia survive routine dawn dissolved oxygen (DO) concentrations of less than 0.3 mg/L, considerably below the tolerance limits for most other cultured fish. In research studies Nile tilapia grew better when aerators were used to prevent morning DO concentrations from falling below 0.7 to 0.8 mg/L (compared with unaerated control ponds). Growth was not further improved if additional aeration kept DO concentrations above 2.0 to 2.5 mg/L.
Although tilapia can survive acute low DO concentrations for several hours, tilapia ponds should be managed to maintain DO concentrations above 1 mg/L. Metabolism, growth and possibly, disease resistance are depressed when DO falls below this level for prolonged periods.
In general, tilapia can survive in pH ranging from 5 to 10 but do best in a pH range of 6 to 9.
Massive mortality of tilapia occurs within a few days when fish are suddenly transferred to water with unionized ammonia concentrations greater than 2 mg/L. However, when gradually acclimated to sublethal levels, approximately half the fish will survive 3 or 4 days at unionized ammonia concentrations as high as 3 mg/L. Prolonged exposure (several weeks) to un-ionized ammonia concentration greater than 1 mg/L causes losses, especially among fry and juveniles in water with low DO concentration. The first mortalities from prolonged exposure may begin at concentrations as low as 0.2 mg/L. Un-ionized ammonia begins to depress food consumption at concentrations as low as 0.08 mg/L.
Nitrite is toxic to many fish because it makes the hemoglobin less capable of transporting oxygen; chloride ions reduce the toxicity. Tilapia are more tolerant of nitrite than many cultured freshwater fish. When dissolved oxygen concentration was high (6 mg/L) and chloride concentration was low (22 mg/L), the nitrite concentration at which 50 percent of the fish died in 4 days was 89 mg/L as nitrite. In general, for freshwater culture the nitrite concentration should be kept below 27 mg/L as nitrite. As a safeguard against nitrite toxicity in recirculating systems, chloride concentrations are often maintained at 100 to 150 mg/L chloride.
Tilapia are more resistant to viral, bacterial and parasitic diseases than other commonly cultured fish, especially at optimum temperatures for growth. Lymphocystis, columnaris, whirling disease, and hemorrhagic septicemia may cause high mortality, but these problems occur most frequently at water temperatures below 68o F. Ich, caused by the protozoan Ichthyopthirius multifiliis, can cause serious losses of fry and juveniles in intensive recirculating systems.
External protozoans such as Trichodina and Epistylis also may reach epidemic densities on stressed fry in intensive culture. In recent years the bacterial infection Steptococcus inae has caused heavy losses, primarily in recirculating and intensive flow-through systems.
1.2 STATEMENT OF PROBLEM
Tilapia is a common species of fish harvested at river Wudil, Kano State. Some harvest them for consumption while some for fish farming. It is therefore desirable to have an idea on the size of a tilapia that has actually reached maturity or ready for harvest, their kinds of feeds, growth pattern and as well how and what they need to reproduce successfully. This study will give researchers and fish farmers’ information important for careful selection and on the general life of tilapia species.