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2 AQUACULTURE FIS 309 (3 Units)

3 Course Outline Sources of water for Aquaculture Fertilization and Liming

4 Sources of Water There are two principal sources of water that can be used in fish farming – ground water and – surface water

5 Surface waters have the advantage of being well oxygenated although they may be polluted from different sources. Surface waters include – lotic waters (steams, brooks, rivers), – lentic waters (lakes, ponds) and – salt or brackish waters. Rainfall and run-off may also be included but since they are highly seasonal, they should be used with caution if they are the sole source of water.

6 Lotic waters have high oxygen content because the water turbulence encourages gaseous exchange, except when they become slow flowing. They usually have some form of organic allochthonous production which may serve as food for the cultured species. However, they often carrying a high load of suspended solids, some of their natural fauna may be parasitic or the cultured species and the indigenous species may be carriers of disease.

7 Salt and brackish waters share the problems of both lotic and lentic waters, and, in addition, are corrosive to many metals. Consequently, special materials will have to be used for pipes, tanks and other equipment.

8 Ground waters are usually pollution free although some may contain noxious gases like hydrogen sulphide and methane, as well as toxic metals. The level of noxious chemicals contained in groundwater is highly correlated to the geology of the area. The major disadvantage of groundwaters is their low dissolved oxygen content.

9 Ground waters include – springs, depressions below the water table and wells. – Depressions are uncommon and their use is questionable since water disappears when the water table drops. – Wells can be free-flowering (artesian) or pumped.

10 The Quality and Quantity of Water Water quality The quality and quantity of available water is of utmost importance in fish culture. The quantity of water required will depend on – the fish species to be cultured and – on the management practices (static or flow- through, intensive or extensive

11 If total losses from seepage and evaporation amount to 5.0cm day the additional minimum daily requirement to maintain the level of the hectare pond described above is 500m3 or 500,000litres or 5.81 sec -1

12 If the water supply is from borehole, the discharge capacity of the borehole will indicate whether or not sufficient water will be available. The exact yield of a borehole may not be known until after money has been spent. It is therefore best to seek the advice of a geologist with a working knowledge of the area or to get some information form other people who own boreholes in the area.

13 If the water source is a stream, the quantity of water available can be calculated from the continuity equation. – Q = A.V – Where Q is the quantity of water available (m 3 ), A is the cross sectional area (m 2 ) and V is the velocity (msec -1 ).

14 Table :1 Discharge rate in a canal of different depths and cross-sectional area. Water-depth (m)Wet cross section are (m2)Water transported Msec-1)(m3) 0.10.11232800 0.20.26785700 0.30.4312011100 0.40.6419216500 0.50.8726024400

15 Thus, if a 0.2m deep canal is used to fill 1ha pond (including water to compensate for the initial saturation of the pond) it will take 18750/5700 = 3.3days to fill the pond. If there were 20 ponds, it would take approximately 66 days to fill them. This may be undesirable and consideration will have to be given to providing a reservoir to supply the water. When pipes are used for the canal, a much greater volume can be supplied. The volume of water passing through a pipe is; Water flow = (cross section x 100) / 100 = (r 2 x3.14 x 100)/1000

16 Table 3.2 Water flow in pipes of various diameters Pipe diameter (cm)Water flow 1sec-1 (m3day-1) 2.50.543 5.08.0150 10.011.5690 15.018.01500 20.031.02600 30.070.06000 40.0130.011000 50.0196.017000 60.0280.024000

17 Water quality Criteria for water quality depend on the use to which the water is intended. Hence, what is good for one situation may not be good for another.

18 It must be mentioned that water for aquaculture should be adequate in: – dissolved oxygen, – pH, – temperature and should not contain – excessive dissolved and suspended solids or – toxic substances. It is possible that some water quality problems can be easily solved, hence quality may not be as critical as quantity

19 It is generally agreed that the growth of fish produced in an extensive system without supplementary feed is at the expense of the nutritive flora and fauna of the water body. However, few scientific works have successfully related primary production to fish production (Ryder, 1976). Consequently, prediction of the ability of a natural body of water to produce fish is based on empirical methods

20 The most applicable are the leger-Huet formulae (Huet, 1986). These are the productivity of running water and artificial ponds as: – K = B x L x k(for running waters) – K = 0.1Na x B x k(for artificial ponds)

21 Where – k is the annual productivity (kgkm -1 ) of water course or kgm 2, – B is the biogenic capacity, – I is the average width of the water course (m), – k the coefficient of productivity and – Na the size of the ponds. The biogenic capacity is an expression denoting the nutritive value of the water examined for its feeding qualities for fish.


23 Liming About two weeks before refilling the pond a layer of lime should be spread over the pond bottom Although not a fertilizer, it helps to accelerate decomposition of waste materials and the mobilization of nutrients from the pond soil. It raises the pH above the tolerable limits for disease vectors or eggs and spores of parasites, thus assisting in their eradication. UNAAB23IKENWEIWE N.B (PhD)

24 Lime comes in several forms and the application rates depend on the pH of the soil and the type of time used. In ponds where the soil pH is around neutral the application rates are of the order listed below. – Crushed limestone-CaCO 3 1200kg ha -1 – Agricultural lime- CaCO 3 2500 kg ha -1 – Hydrated lime -Ca(OH) 2 100kg ha -1 – Quicklime-CaO200 kg ha -1 UNAAB24IKENWEIWE N.B (PhD)

25 If the pond has a pH of about 4.5 or less, approximately 4.5 tonnes of agricultural lime will be required. If the pond had been limed before, subsequent annual liming are usually much less, i.e 20-25% of the initial application rate. Hydrated lime is the best because it tends to be the most concentrated and cheapest form. Care should be taken if quicklime is used because it can burn on contact with the skin UNAAB25IKENWEIWE N.B (PhD)

26 Fertilization The yield of any fish pond depends on its natural productivity, which is linked to nutrient availability in the pond soil and water. It thus allows an increase in fish density without the need for supplementary feeds. The most important nutrients for growth of food organisms are phosphorus (P), nitrogen (N) and potassium (K). if there nutrients are in short supply or absent they can easily be increased by fertilization using organic and inorganic substances. UNAAB26IKENWEIWE N.B (PhD)

27 Fertilizers are applied to the pond water or soil to stimulate and maintain plant growth and establish the secondary food chain. However, the mechanism of organic and inorganic fertilizers in achieving this production are quite different. UNAAB27IKENWEIWE N.B (PhD)

28 INORGANIC FERTILIZERS Inorganic fertilizers are usually of chemical origin that dissolve in the pond water and provide nutrients almost immediately. This stimulates phytoplankton (algal) growth and zooplankton production, both of which are direct sources of food for fish UNAAB28IKENWEIWE N.B (PhD)

29 the main limiting element in established ponds is phosphorus and this can be provide in several forms, including basic powdered single superphosphate or granular triple superphosphate UNAAB29IKENWEIWE N.B (PhD)

30 ORGANIC FERTILIZERS Organic fertilizers are usually waste plant or animal products include manure from cows, sheep, ducks, chickens and humans and grasses the non-utilized parts of crops such as rice husks that have rotted down this mechanism of fertilization is the basis of integrated fish farming. The important points to remember about organic fertilizers are slowly as they rot down and release the nutrients. UNAAB30IKENWEIWE N.B (PhD)

31 Applying the fertilizer There are several ways of applying the fertilizer. In drained which are just about to be filled both organic and inorganic fertilizers can be spread over the pond bottom. In a pond which has been filled and stocked with fish the usual way for inorganic fertilizers such as superphosohates broadcast it evenly over the pond surface. UNAAB31IKENWEIWE N.B (PhD)

32 NON DRAINABLE PONDS In ponds that cannot be drained or insufficient water is available to refill it, conditioning is no less important. In this case sediments wastes which have accumulated on the bottom of the pond during the grow-out season should be scraped out and placed on the bank or surrounding fields. UNAAB32IKENWEIWE N.B (PhD)

33 If necessary quicklime is broadcast over the ponds at a rate of approximately 600kg ha-1 and then fertilized according to the procedures described for drainable ponds. UNAAB33IKENWEIWE N.B (PhD)

34 Water Quality Maintenance The survival, growth and consequent production o fish depend, to a large extent, on the physical, chemical and biological status of the water in the culture enclosure. Every cultured fish species has its own peculiar water quality requirements UNAAB34IKENWEIWE N.B (PhD)

35 Man has very little control over salinity of fish ponds. It is therefore imperative to culture a fish in a salinity medium in which it naturally occurs Other critical features of the holding unit that will influence production include water depth, transparency, dissolved on concentration, alkalinity, free dissolved carbon dioxide, odour and levels that will favour high fish production UNAAB35IKENWEIWE N.B (PhD)

36 DEPTH Depth of water in the pond must be kept steady through regular replenishment with fresh and clean water to top up for water lost by seepage and evapotranspiration. If water level is not uncontrolled, it may overflow and eventually break down the dam or the dyke. UNAAB36IKENWEIWE N.B (PhD)

37 TRANSPARENCY The Secchi disc is the instrument sued for measuring turbidity or transparency. A high transparency (>80cm) is an index of low production. This can be improved by adding fertilizers. Low transparency (<20cm) may be de to suspended silt, clay, plankton or organic matter. This also encourages low fish production. UNAAB37IKENWEIWE N.B (PhD)

38 DISSOLVED OXYGEN High phytoplankton production may reduce dissolved oxygen content in the pond water at night because they use oxygen for respiration but do not product it by photosynthesis. The dissolved oxygen content is inversely proportional to temperature, and high temperature during the early afternoon may cause the oxygen content to fall below the critical level. It is recommended that the dissolved oxygen level is measured in the early morning and again around 14.00 hrs. For minimal stress and good growth it should be above 4-5mg 1-1. UNAAB38IKENWEIWE N.B (PhD)

39 Aeration Aeration can be achieved in a number of ways, but the method used will depend on financial resources, access to electricity and intensity of production. It can be achieved with electrically driven paddle wheel agitators or similar device which cause good mixing of the water and allow gaseous oxygen to dissolve in the water and carbon dioxide to escape. UNAAB39IKENWEIWE N.B (PhD)

40 pH Water with a pH range of 6.5-8.0 is most suitable for fish production low pH can be improved through the addition of lime high pH can be lowered through addition of ammonium sulphate, ammonium nitrate and urea fertilizers. UNAAB40IKENWEIWE N.B (PhD)

41 POLLUTANTS With industrialization, intensification of agriculture and widespread industrial and agro- chemicals and detergents, it is inevitable that some waste products of these ventures find their way into local surface underground water bodies by run-off or seepage, and eventually into ponds. As a rule, water flowing ponds must be analyzed routinely for pollutants. If the water in the found to be polluted, it should be drained and replenished with fresh clean water, preferably from an alternative source. UNAAB41IKENWEIWE N.B (PhD)

42 Weed control Weeds are macroscopic plants and macrophytes whose existence, especially in large quantities, may interfere with pond management operations such as feeding, test cropping and testing. They compete with phytoplankton for available nutrients depriving planktivorous fishes of their natural food, provide havens pests and encourage evapotranspiration. UNAAB42IKENWEIWE N.B (PhD)

43 Aquatic weeds include plants, e.g Pistia stratiotes (water lettuce), pond weed (Lemma sp) filmentous algae, submerged weeds, e.g Ceratophyllum,emergent water lily (nymphea lotus) and marginal or fringe vegetation Submerged and emergent weeds can be effectively checked through fertilizer application.

44 Copper sulphate and synthetic algicides e.g. simazine and Aquazine can be used to control excessive growth of filamentous algae and phytoplankton. The use of copper sulphate and synthetic algicides also create low dissolved oxygen levels after their application. Synthetic algicides tend to have longer residual action when compared with the use of copper sulphate in the control of filamentous algae and phytoplankton. UNAAB44IKENWEIWE N.B (PhD)

45 Biological control of aquatic weeds through the introduction of grass eating fish such as grass carp (Ctenopharyngodon idella), Tilapia zillii and Heterotis niloticus is most often recommended in polyculture systems. Aquatic weeds can also be controlled through manual removal or mechanically through the use of specially designed amphibious machines.

46 Routine production activities Stocking The main objective of fish farming is the sustained production of a good yield of fish from the production unit, For sound production scheduling the stocking rate should be calculated accurately base on the expected grow increment and mortality over the growing season. Expected output from pond Number to be stocked = ---------------------------------------- x survival rate Expected increase in weight of individual fish UNAAB46IKENWEIWE N.B (PhD)

47 General rules which apply when transferring fish from one place to another. Check the disease status of the fish prior to introduction to avoid contamination. If possible starve the fish for 24 hours before movement Handle the fish as little as possible Prevent the fish form becoming too warm through exposing to sunlight. Stock or transfer the fish in the early morning when the temperatures are lower and the fish less active. Provide the fish with plenty of oxygen/air if they are being transferred over long distances. UNAAB47IKENWEIWE N.B (PhD)

48 Further Readings Olokor, J.O., J.A. Ihuahi, F.S. Omojowo, B.A. Falayi and E.O. Adeowo (2007). Hand book of Practical Fisheries Technology. Fisheries Technology Division, Remi-Thomas Press

49 Thank you


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