Literature_review_2.1_fertilization (1).pdf

LITERATURE REVIEW

2.1 FERTILIZATION Pond fertilization is based on the notion that the addition of nutrients to the water will increase the production of plankton (microscopic plants and animals). This increase in the amount of fish food then results in increased fish production (pounds of fish per acre). While fertilization may increase fish production and help control aquatic vegetation due to water clouding caused by dense plankton blooms, the disadvantages of fertilization usually outweigh the advantages

Type of Fertilizer According to Diana et al. (1994) traditional inorganic fertilizers for land application contain a combination of nitrogen, phosphorus, and potassium, usually expressed in percentages. For example, a common fertilizer grade is 20-16-8 NPK, having 20% N, 16% P, and 8% K, or yielding 20% N, 7% P, and 6.6% K by weight. Experiments have not demonstrated a need for potassium to stimulate production, and nitrogen and phosphorus ratios in mixed fertilizers are not generally appropriate for pond aquaculture. Most commonly, pond fertilization is done by applying nitrogen and phosphorus compounds separately. Typical materials for nitrogen include urea, sodium nitrate, ammonium nitrate, and calcium nitrate, while phosphorus is added as superphosphate, triple super phosphate (TSP), monoammonium phosphate, and diammonium phosphate (Lin et al. 1997). Some products result in excess ammonium, and problems with water quality, and may negatively affect pH. Most commonly, TSP and urea are added as fertilizers when inorganic materials are used.

Animal manures are not the only organic waste product used in aquaculture; waste plant material composed of agricultural byproducts, other waste terrestrial vegetation, and even aquatic vegetation have at times been used in composting systems as fertilizers. These are favored in some cultures due to lack of availability and high price of animal manures (Little et al. 1995). Animal manures used in fish production include human, buffalo, cattle, goat and sheep, pig, duck, and poultry (Lin et al. 1997). Chicken manure has commonly been used to stimulate tilapia growth, while pig and duck manure is common in integrated farming systems with ducks grown on ponds or pigs grown in structures above ponds

Studies evaluating fertilizers and their impacts on secondary production have often demonstrated that organic manures stimulate secondary production much more than inorganic fertilizers do, as organic matter, fecal matter, and waste feeds found in manures stimulate heterotrophic bacteria and decomposing invertebrates (Diana et al. 1994). Fertilization to enhance secondary production may be best done with organic fertilizers.

Fertilization Rates Traditional fertilization rates used before 1980 were considerably lower than rates used today. Studies based on a variety of culture systems indicated that nitrogen fertilization was not required in ponds, and phosphorus loadings were relatively low (Dania et. al., 1994). Overall annual fish yield in this experiment was about 800 kg/ha. However, these studies were based on relatively low stocking densities with fish that are benthivores. Subsequent studies as part of Aquaculture Collaborate Research Support Program (CRSP) have shown that considerably greater primary production and tilapia production can be achieved with higher rates of nitrogen and phosphorus fertilization. The best fertilization rate determined by

CRSP was considerably higher than fertilization in these previously studied ponds. Fish stocking rates in most of our experiments were 10,000–20,000 tilapia/ha, and annual fish yields of 3000–5000 kg/ha These high production levels require higher fertilization rates. Experiments to be described later showed nutrient balance of 4 N:1 P and daily application of 4 kg N to 1 kg P/ha resulted in optimal fish production with fertilizers and no feed in Thai tilapia ponds (Knud-Hansen et al. 1993). Ponds fertilized to such a high degree reached a hyper-eutrophic state with phytoplankton standing crops >13 mg/L dry biomass. Again, these production rates and plankton biomasses were considerably higher than earlier experiments. Results of these experiments remain controversial.

Experiments in Honduras (Teichert-Coddington et al. 1992) and Thailand (KnudHansen et al. 1993) supported high fertilization rates and N:P balances of 4–6:1 (Diana et al. 1994; Lin et al. 1997). However, Boyd (2003) still considered these rates too high for tilapia production and believed they would cause water quality problems. High rates used in Honduras and Thailand did not deteriorate water quality or require management such as flushing or aeration. Subsequent experiments in deep ponds (Diana and Lin 1998) further supported these high fertilizer rates and indicated ponds should be fertilized on a per-unit-area basis, rather than a per-volume basis. However, nutrients in drained water at harvest could create problems, and water should be retained or reused if possible (Lin et al. 2001).

After establishing rates, experiments assessed frequency and other fertilizer application methods. Standard CRSP experiments used weekly nutrient additions, in either inorganic or organic form, depending on the experiment. The intent was to keep all nutrient concentrations high so log-phase phytoplankton growth would

occur. Fertilization frequency may be changed to save on labor, but must be balanced with pond nutrient conditions. Less frequent fertilizer application at the same daily rate could cause water problems from loading large volumes of materials at one time. Knud-Hansen and Batterson (1994) evaluated fertilization frequency effects on pond culture of tilapia. They used frequencies of daily, twice/week, weekly, twice every 3 weeks, and once every 2 weeks. Daily nutrient loading was 4 kg N and 1 kg P/ha. There was no nitrogen or phosphorus limitation in these inorganically fertilized ponds in any treatment, and fish yield was not dependent on fertilization frequency. This could be extrapolated to indicate fertilizer need only be applied once every 2 weeks. However, more recent experiments have shown individual ponds may vary in nutrient concentrations, and algal bioassays could be used to determine timing and fertilizer amount (Guttman 1991; Lin et al. 1997). The ultimate fertilization goal should be to apply fertilizer at the rate needed by algae, not on a set schedule, if such rates can be reasonably determined.

Beyond issues with fertilization frequency, application methods are also important, particularly with inorganic fertilizers. Organic matter in most manures and compost decompose slowly and release nutrients over a week or more. These materials accumulate on the bottom and release their minerals slowly. However, many inorganic materials are also designed to slowly release minerals. When these fertilizers sink to the bottom, minerals such as phosphorus may become bound to sediment. As a result, considerable phosphorus is lost from these fertilizers. Overcoming this loss may involve using liquid fertilizers, suspending fertilizer in a bag, or pulverizing the material to increase solubility. All these methods are intended to dissolve more available phosphorus and nitrogen where it can be taken

up more efficiently by phytoplankton. Using more soluble fertilizers may also require more frequent fertilizer application.

2.2 LIMING This is the act of introducing lime in the pond. Lime is considered as fertilizer, since; it supplies calcium, which is an essential nutrient. The objective of liming is to neutralize acidity in the upper layer of bottom soil and to increase concentrations of total alkalinity and total hardness in the water. Several studies have shown positive responses in phytoplankton productivity and fish production following liming of acidic ponds, and methods for determining the lime requirements of bottom soils have been developed (Boyd, 1995). Nevertheless, liming often is applied to ponds indiscriminately, with no concern for bottom soil pH or total alkalinity and total hardness concentrations. It is doubtful that liming has a large influence where soil pH is above 7 or total alkalinity is above 50 mg L-1 (Boyd, 1995). According to Abowei (2010), the importance of lime application in fish ponds include: 1. It increases the alkalinity of water thereby increasing the availability of carbon (iv) oxide for photosynthesis. 2. It increases the pH of pond bottom mud and water, which enhances the availability of nutrients like phosphorus. 3. The increased alkalinity values after liming provides a buffering capacity to pond water against drastic pH fluctuation resulting from eutrophication. 4. Through the increased nutrient availability, the production of benthic organisms increases. 5. Humus strains of vegetative origin restrict light penetration into the pond water and are cleared by lime treatment.

6. Destroys bacteria as well as, fish parasites in their various life history stages.

Type of lime: The four common types of limes used are: 1. Agricultural limestone (CaCO3) 2. Slaked lime (Ca(OH)2) 3. Quick lime (CaO) 4. Calcium cyanide

Limes differ in their ability to neutralize acid. Agricultural limestone is used as a standard for other limes. The neutralizing value of CaCO3 is 100%, Ca(OH)2 is 136% and CaO is 179%. Calcium cyanide is seldom used. Agricultural limestone is the most commonly used lime in fishponds. When Ca (OH) 2 and CaO are used, enough time should be allowed before stocking the pond. This allows an appreciable reduction in the PH raised by the lime. Otherwise the fish dies (Abowei et. al., 2011).

Application of lime: When the pond is new, lime is spread evenly on the pond bottom before filling with water. The lime requirement of pond bottom soil is determined before liming. Nursery ponds are limed to eradicate predatory organisms, parasites and other disease causing organisms. Older ponds containing water can be limed by spreading lime over the entire pond surface. For small ponds, broadcast lime from the dykes while in large ponds, construction of platforms or use of boats become necessary (Dulbin-Green, 1990). The dosage depends on the soil type in the pond bottom. The aim of liming is to bring the pH to neutral value. This can be achieved through a careful study of soil type and the

pH. For example, more lime is required for clay soils than sand soils. Acid sulphate soils have greater lime requirement (Dulbin-Green, 1990). It is advisable to leave the pond dry for at least two weeks after lime application. Subsequent application may be necessary for fresh water ponds because of the residual effects of lime. In ponds with acid sulphate soils of pH 4.5 or less, the lime requirement is high. So the application of more than two installments is necessary. However, extensive use of lime in reducing acidity of acid sulphate soils is not economical because large quantities of lime are required (Dulbin-Green, 1990). He recommended repeated flushing and draining of ponds using tidal waters until an ideal pH for pond water (6.5-7.0) is reached. He also recommended the use of small quantities of agricultural lime scattered on dyke slopes from time to time (Dulbin-Green, 1990).

2.3 FEEDING Essential or indispensable amino acids (EAAs) cannot be synthesized by fish and often remain inadequate but are needed for growth and tissue development (Wilson et al., 1995). Fishmeal is known to contain complete EAA profile that is needed to meet the protein requirement of most fish species. Since fishmeal is expensive as a feed ingredient, the use of nonconventional feedstuffs has been reported with good growth and better cost benefit values. The utilization of nonconventional feedstuffs of plant origin had been limited as a result of the presence of alkaloids, glycosides, oxalic acids, phytates, protease inhibitors, haematoglutinin, saponegin, momosine, cyanoglycosides, linamarin to mention a few despite their nutrient values and low cost implications (Sogbesan et al., 2006). Nonconventional feed resources

(NCFRs) are feeds that are not usually common in the markets and are not the traditional ingredients used for commercial fish feed production (Madu et al., 2003). NCFRs are credited for being noncompetitive in terms of human consumption, very cheap to purchase, byproducts or waste products from agriculture, farm made feeds and processing industries and are able to serve as a form of waste management in enhancing good sanitation. Abowei and Ekubo (2011) explained that for many years water quality has been the most important limitation to fish production. Advances in life support technology have been substantial in recent years, and nutrition is increasingly regarded a key limitation to increased production efficiency as well as the growth and propagation of “new” species. Commercially prepared diets for channel catfish and salmonids have been developed using a great deal of research data on specific nutritional requirements of these species, their production systems and their life stages. Some nutritional studies have also been carried out for tilapia production. For all other species, including freshwater and marine ornamentals, nutritional management is based on a combination of application of knowledge generated for the species mentioned above and the experience of successful aquarists (CAN, 1993).

Most successfully reared ornamental fish are omnivores, and these are the species that have adapted best to captive conditions, including available nutrition. Successful maintenance of “difficult” species is often influenced by the aquarist's success in obtaining or rearing specialized food items. For example, members of the highly popular sygnathid family, sea horses and sea dragons, have long, tubular mouth parts. These animals are not physically capable of ingesting typical commercial fish foods. Instead, successful husbandry typically involves significant investment in the rearing of brine or mycid shrimp. The popularity of these animals

has made the extra investment worthwhile for many commercial exhibits, but makes it unrealistic for the typical home aquarist (Helfrich and Smith, 2001).

Generally, fish diets tend to be very high in protein. Foods for fry and fingerlings frequently exceed 50% crude protein. As growth rate decreases and fish age, protein levels in diets are decreased accordingly. Protein levels on growout diets often approach or exceed 40% crude protein, while maintenance diets may contain as little as 2535%. In addition to decreasing the protein content of the food as fish grow, the particle size must also be changed. Many fish require live food when they are hatched because their mouth parts are so small. Some fish, such as the channel catfish, are large enough to place on a fry diet immediately without having to bother with the expense and labor needed for live foods (Houlihan et al., 2001).

Fish meal should be a major protein source in fish diets. There are essential amino and fatty acids that are present in fish meal but not present in tissue from terrestrial plants or animals. Low cost formulations in which fish meal has been eliminated and replaced by less expensive proteins from terrestrial sources (soybeans) are not recommended for fish. Fish meal and fishery byproducts have high lipid content and therefore rancidity can be a problem if foods are not properly stored. In addition to the concern for essential amino acids that may be present in fish meal, fish require long chain fatty acids (C20 and C22) that are not found in tissue from terrestrial organisms. Fish meal, shrimp meal and various types of fishery byproducts are the source for these essential fatty acids. In addition, crustacean byproducts serve as a source of carotenoid pigments that are excellent for color enhancement. There is a high oil content associated with carotenoid pigments, so vitamin E supplementation is recommended when these are used.

Vitamin and mineral requirements of most fish species are not well understood. It is known that fish absorb minerals from the water. Calcium deficiency of channel catfish fry has been associated with calcium concentrations less than 10 mg/L in rearing systems. Calcium chloride has been used to raise the calcium concentration of water used for fry rearing. Conversely, too much calcium in the water has been associated with reproductive problems in some Amazon fish. Water hardness > 100 mg/L has been attributed to formation of hard shells for eggs of some tetra species, and fry were not able to hatch (Roberts, 1999).

Most fish require dietary ascorbic acid (vitamin C). This becomes very important if fish are reared in a poorly lit area where algae cannot grow, or if they are so crowded that they cannot consume any natural food items that might be in the water. Ascorbic acid added to fish foods should be phoshorylated to stabilize the vitamin and increase storage time. In addition, vitamins A, D, E and B complex should be added to fish foods. The concentration of vitamin E is often inadequate, especially in diets that are high in fat. If fish are housed in natural systems with algae and phytoplankton, and stocking rates are not too great, then vitamin supplementation seems to be less important, presumably because of the availability of natural food items (Robinson et al., 1998).

Because fish feeds usually contain relatively high amounts of fish meal and/or fish oil, they are very susceptible to rancidity. In addition, ascorbic acid is highly volatile, but critical to normal growth and development of most species of fish. For these reasons, fish feeds should be purchased frequently, ideally at least once a month and more frequently if possible. Feeds should be stored in a cool, dry place and should never be kept on hand for more than three months. Refrigeration of dry

feeds is not recommended because of the high moisture content of that environment. Vitamin C is an essential vitamin for fish, and most species tested are not capable of synthesizing their own. Stabilized (phosphorylated) forms of ascorbic acid are available and are used in many, but not all, fish feeds. Feeds that do not contain stabilized ascorbic acid are not recommended for fish. If assays for ascorbic acid content are to be run it is imperative to know which form the vitamin is in before sending the feed sample to a laboratory (Winfree, 1992).

Commercially milled fish foods are usually sold as dry or semi-moist pellets or as flakes. Pellets are typically the most complete diets. They are cooked, and, if marketed as a complete ration, the nutrition in each particle should be uniform. Disadvantages include the potential for rapid sinking unless the pellet is extruded. In addition, the pellet size is very important. It may be impossible to manufacture a particle small enough for some fish, especially juveniles of many species. For larger animals, a very small pellet may be unacceptable.

2.4 DISSOLVED OXYGEN The principal source of oxygen that is dissolved in water is by direct absorption at the air-water interface which is greatly influenced by temperature (Kutty, 1994). At low temperature more oxygen diffuses into the water. The solubility of oxygen in

water is controlled by some major factors such as temperature, salinity, pressure and turbulence in the water caused by wind, current and waves. Surface agitation of water helps to increase the solubility of dissolved oxygen in water . In rivers and streams the turbulence ensures that oxygen is uniformly distributed across the water and in very shallow streams the water may be supper saturated (Abowei, 2010). Oxygen concentration in water is controlled by four factors: photosynthesis, respiration, exchanges at the airwater interface, and supply of water to the water body or pond (Erez et al., 1990). Dissolved oxygen concentration of 5.0 mg/L and above are desirable for fish survival (Boyd, 1998). Low dissolved oxygen concentrations are known to be one of the major problems to faunal and floral survival in the aquatic environment. Low concentration of dissolved oxygen created anoxic condition within the Black and Baltic Sea (SaizSalinas, 1997). The problems of anoxia are the major causes of faunal depletion in aquatic ecosystems.

2.5. PH The pH scale ranges from 0 to 14. The pond water is neutral when the pH is exactly 7. This means that the solution contains an equal concentration of H+ and OH- ions. Substances with a pH of less than 7 are acidic. This contains a higher concentration of H+ ions. Substances with lower pH are more acidic. Substances with a pH more than 7 are basic. This contains a higher concentration of OH - ions than H+ ions. Substances with higher pH are more basic. A universal indicator is made up of a mixture of various indicators which function at different pH ranges. By series of successive color changes, it can indicate pH values from 3 to 11. These pH changes can be easily determined by comparing the colors obtained with that of the standard given. Litmus is a substance that turns red when in contact with acidity and blue when in contact with basicity.

These methods of measuring the pH, is not very accurate. A pH meter is an electrical device with electrodes that are very sensitive to hydrogen H+ and hydrogen ions. It can measure the pH of very dilute solutions as well as that of colored and opaque liquids. The colorimeter also measures pH. Colorimeters have discs with different range of pH. There are two compartments. One tube with sample water is kept in the left compartment. The other tube with the indicator is kept in the right compartment. The color disc is then rotated until the two colors match. The value can then be red. pH higher than 7, but lower than 8.5 is ideal for biological productivity while pH lower than 4 is detrimental to aquatic life (Abowei, 2010). Most organisms including shrimps do not tolerate wide variations of pH over time and if such conditions persist death may occur. Therefore, waters with little change in pH are generally more conducive to aquatic life. The pH of natural waters is greatly influenced by the concentration of Carbon (IV) oxide which is an acidic gas (Boyd, 1998). Phytoplankton and other aquatic vegetation remove carbon (IV) oxide from the water during photosynthesis, so the pH of a water body rises during the day and decreases at night (Boyd and Lichtkoppler, 1979). Rivers flowing through forests have been reported to contain humic acid, which is the result of the decomposition and oxidation of organic matter in them hence has low pH. In the open ocean the pH of sea water falls within limits of 7.5-8.4. Waters with low total alkalinity often have pH values from 6.5-7.5 before day break, but when phytoplankton growth is high, afternoon pH values may rise to 10 or even more (Beasley, 1996). Changes in the acidity of water can be caused by acid rain, run-off from surrounding rocks and waste water discharges (Ibiebele et al., 2003). Waters with pH values of 6.5 to 9.0 are considered best for fish production, while the acid and alkaline death points are 4.0 and 11, respectively. Low pH values or acidic waters are known to allow toxic

elements and compounds such as heavy metals to become mobile thus producing conditions that are inimical to aquatic life (Gietema,1992). The nitrogenous compounds often present in water are trioxonitrate (v), nitrogen (iv) oxide and ammonia. Trioxonitrate (v) and nitrogen (iv) oxides are among several oxides of nitrogen. The formation of these oxides by the direct combination of nitrogen and oxygen requires very high temperatures. Because of the large amount of energy required for their formation, these oxides of nitrogen are readily interconvertible, and are easily decomposed of their elements. Ammonia is a hydride of nitrogen. In nature, ammonia is produced when nitrogenous matter decays in the absence of air. The decomposition may be brought about by, heat or putrefying bacteria. As a result, small traces of ammonia may be present in the air. However, because of its great solubility in water, it rapidly dissolves in rainwater and finds its way into the soil where it may be converted into other compounds (Ekubo and Abowei, 2011). Trioxonitrate (v) ion (NO3-), nitrogen (iv) oxide ion (NO2-) and ammonium ion (NH4+) are products from the accomplishment of nitrification by two different groups of bacteria functioning in sequence. The first group converts ammonium ions to nitrogen (iv) oxide ions, and the second group converts this nitrogen (iv) oxide ion to trioxonitrate (v) ion. The trioxonitrate (v) ion released into the water by bacteria, can be picked up by, the roots of aquatic plants. Most of the trioxonitrate (v) ion in the root is quickly incorporated into organic nitrogen compounds and then stored in the cell vacuoles or transported to other parts of plant body through the vascular tissue. The nitrogen compounds in the plant body may eventually be broken down to ammonia by decomposers when the plant dies or when an animal that consumed the plant dies or excrete it. Ammonia as products of biological processes can be related to pollution of the water. Over fertilization or enrichment of the ponds, incomplete degradation of faecal matter and feed

remnants cause high ammonia levels in fishponds (Aboewi, 2010). Un-ionized ammonia (NH3) is toxic to fish but the ammonium ion (NH4+) is not toxic. Unionized ammonia is highly toxic at levels less than 1 mg/L. Tropical species can withstand higher toxicities. Mead (1995) reported that unionized ammonia was 300-400 times more toxic than NH4+. The effect of toxicity is higher at higher pH. Estimation of nitrogenous compounds: Of the several procedures adopted in ammonia determination, the implest is the direct nesslerization method. This employees the use of colorimeter. The other intermediate products, trioxonitrate (v) and nitrogen (iv) oxide are all estimated calorimetrically using the Bausch and Lomb Mini Spectro Kits. Nitrogen (v) oxide is present in natural waters only in small quantities. It has been found to be toxic to fish, as NO2 combines with haemoglobin, and forms methylhaemoglobin causing the brown coloration of blood (Russo et al., 2007). In contrast, ammonia and nitrate toxicity increases at lower pH levels (Russo et al., 2007). EIFAC (2006) therefore recommended that levels of pH, calcium content (bicarbonate hardness) and chloride content (salinity) should be indicated when reporting on nitrogen (v) oxide concentrations. Wickins (1981) suggested that nitrogen (iv) oxide concentration in hard fresh water pond should not exceed 0.1 mg NO2- N/L and in salt water 1.0 mg NO2-N/L.