Fish Farming Systems Introduction PDF

4. Fish Farming Systems Introduction Classification of systems Several ways:  Based on salinity (freshwater, brackish, seawater)  Based on intensity  Extensive  Least managed form  Large ponds are used for farming  No supplemental feeding or fert...

4. Fish Farming Systems Introduction Classification of systems Several ways:  Based on salinity (freshwater, brackish, seawater)  Based on intensity  Extensive  Least managed form  Large ponds are used for farming  No supplemental feeding or fertilization is provided  Semi-intensive  Smaller ponds  Higher stocking density  Natural food developed by fertilization with/without supplemental feeding  Intensive  Well-managed form  Achieve maximum production with minimum quantity of water  Small ponds/tanks/raceways with very high stocking density Classification of systems  Based on how many species are stocked:  Mono-culture  One species  Poly-culture  Many species (No negative interactions. Different feeding habits)  Based on facilities  Ponds  Cages  Pens  Raceways  Tanks/RAS Ponds (https://www.fao.org/fishery/docs/CDrom/FAO_Training/FAO_Training/General/x6708e/x6708e01.htm)  Ponds should be: inexpensive to construct, easy to maintain and efficient in allowing good water and fish management.  Receive water from various sources (stream, rain, spring, etc)  Can be earthen, walled (e.g bricks or cement).  Mono/poly culture – can be integrated with agriculture. Barrage pond Diversion pond Ponds  The main advantage of pond fish culture is that the protein requirement of fish is largely satisfied by the ‘natural’ food sources.  Size of ponds determines the fish density and available oxygen – also amount of waste products.  Ways to increase products: introduction of fresh water, aeration, protection against predators.  All fish are harvested at the end.  Major disadvantage is the role of weather. Cages  Effective use of large natural water bodies  Relatively simple and low-cost system  Easy management  Main disadvantage is the large effect of external factors (e.g weather, predators, wild fish)  Multiple harvests Cages - fouling Cages - fouling  Chemical method (slow release of toxic substances and formation of a thin ‘membrane’ around nets)  Biological method (co-farming of other aquatic organisms)  Use of resistant materials Antifouling - Int. J. Mol. Sci. 2014 Disadvantages  Untreated nets are safe for the environment.  Frequent cleaning and replacement of nets cause stress to the animals, damage the nets, increase maintenance costs and decrease profit margins.  The direct economic cost to the aquaculture industry of controlling biofouling = 5 – 10% of production cost. Pens  Look like cages, but the bottom is not closed (could be just the bottom of the lake or river)  A hybrid system between pond and cage.  Increased flexibility of size and production.  Fish can use food sources from the bottom.  Still vulnerable to external factors. Raceways  A flow-through system  A series of large concrete or earthen ponds.  Ponds can be arranged in sequence or parallel – higher risk of disease problems when in sequence! Tanks/Recirculating Aquaculture System (RAS)  Complete or partial reuse of water – need to restore the quality of influent water!  Addition (about) 10% of ‘new and clean’ water.  Ability to monitor and regulate many factors.  Highest socking density and production.  Highest cost – must maintain optimum water quality.  Tanks  The shape, color, depth and volume of tanks should be appropriate for the species and life stage.  They should have smooth, inert, sealed interior surfaces.  Tanks should be self-cleaning, or adequate means for the regular cleaning of tanks.  They should be equipped with a covering that prevents fishes from jumping from the tank. Ostrander GK. (2000) The Laboratory Fish  Stocking density  ‘Real densities’.  Species (e.g. schooling species).  Maintain high oxygen levels (near saturation).  Ammonia.  Spread of pathogens. Classification of systems Integration with agriculture or animal farming  The output from one sub-system (otherwise wasted) becomes an input to another sub-system resulting in a greater efficiency of output of desired products from a specific land/water area  Example of plants are rice, banana, coconuts, etc.  Feces and other wastes from animals , like pigs, chicken, are used by fish.  High risk of transmitted diseases to other humans, when terrestrial animals are integrated. Jobling, M. (2010). Farmed species and their characteristics. Chapter 4. In N. R. François, M. Jobling, C. Carter, & P. U. Blier (Eds.), Finfish aquaculture diversification (p. 681). Oxfordshire, UK: Water quality and treatment Filtration of incoming water  Mechanical filtration. Separation of solids and liquids. The simplest type comprises a static screen, a grating or perforated plate. They are usually simple in operation and relatively easy to maintain. In sand filters, water is allowed to flow through a layer of sand with particles of varying sizes and depth. The layer is not dense, but contains a number of channels and holes created between the particles that constitute filter medium.  Gravitational filtration Gravitational filtration utilizes the force of gravity to separate particles from fluid. Density difference of the suspended particles and water is used in this type of filtration. A simple example of gravity filtration is sedimentation. Reducing the microbial load in the water used  Normal microbial load  5 × 105 - 3 × 106 bacterial cells / ml (many non readily culturable).  2 × 106 – 2 × 108 viruses / ml.  Radiation using UV.  3-6 log units reduction.  240-280 nm.  No changes in water quality parameters.  Ozonation.  Competition with other microorganisms. UV radiation UV lamp Ozonation Ozone in the ozone layer filters out sunlight. Ozone is a powerful oxidant (also forms highly reactive chemical agents). It can destroy microorganisms releasing oxygen. Reduce bacterial load by 3-6 log units. High cost and sometimes toxic to fish, especially young ones (lesions to epithelia and blood cells). It can destroy equipment made from pvc and iron. Residuals are eliminated within minutes. Competition with beneficial microorganisms  Mainly hatcheries.  Three basic methods:  ‘Maturation’ of the water.  Constant enrichment with beneficial microbes.  Use of ‘green water’. Reduced dissolved oxygen  Increased water temperature.  Increased oxygen consumption (e.g. increased consumption by plants or algae, mainly due to increased nutrients in the water).  Under intensive farming conditions: increased stocking densities.  Oxygen is transferred inside the body of the fish through the gills and the skin - three steps: ventilation or medium flow past the exchange sites, diffusive transfer between medium and blood and finally, blood flow through exchanging structures. In this transfer, the partial pressures of the oxygen (tensions) are more important than oxygen concentrations.  Depending on the fish species, below a range of 50-70% air saturation (which is roughly proportional to oxygen partial pressure in the water), oxygen uptake is affected.  Tolerance of hyperoxic conditions is species-specific and may also www.vetcare.g r Oxygenation vs Aeration Oxygenation Aeration Higher cost Limited transfer of oxygen into When large amounts are needed the water More appropriate for small When large fish densities systems, with small fish densities Could be as back-up system Not easy to control oxygen levels Aeration/oxygenation Equipment:  Gravity aerator: the water falls under gravity and air is mixed into it from the surrounding atmosphere.  Surface aerator: this type of aerators are commonly used on ponds and can also be used in large tanks, cages etc. They break up or agitate the surface of water. Can cause some damage to fish.  Diffuser aerator: Diffuser aerators inject air or oxygen into a body of water in the form of bubbles. Oxygen is transferred from the bubbles to the water by diffusion across the liquid film. Gas bubble disease  Increased pressure of gasses in the water (mainly nitrogen).  Depending on the fish species, prolonged exposure of fish to moderate supersaturation (