How To Construct A Fish Pond: Principles

a. Most earthen ponds are built with hand labour in Africa. For ponds larger than 1000 m2, heavy equipment is most effective as larger distances to move earth make hand labour costly. Work crews building fish ponds require close supervision for quality pond construction. b. top soils are removed from the site, later to be placed on top of dikes for sowing with grass cover c. a general survey of the site showing elevations, angles and distances is useful for designing the fish farm pond lay out, showing water canals and drainage canals. Ponds should be staked out with pegs to show pond lay out for tops and bottoms of dikes. d. The shallowest depth for production ponds should be no less than 60-80 cm and the deepest waters should be at least 1.2 m to 1.5 m depending on the slopes. Brood ponds for reproduction should be more shallow e. pond bottoms are hard and clean without stumps or obstructions and slope gently towards the central drain. f. pond dikes are to be compacted every 15-20 cm of soil depth. Compaction is very important and cannot be forgotten. Manual compaction is done with laborers using earth compactors or dammers and will assure no seepage of water. This will later minimize water use and greatly reduce repairs and maintenance costs. Dikes can be washed out from leaks that enlarge as water flows through them. g. the most efficient and low cost pond construction uses dug soils (cut) to build (fill) the dikes. So “Cut should equal Fill”. h. Slopes on the inside dikes should be 2:1 up to 3:1, whereas outside slopes could be steeper at 1.5:1 to 2:1. Gentle slopes require less maintenance and lower cost in the long run. i. the dike height between the water level and top of the dike is called the Freeboard and should be 15-30 cm depending on pond size. Standpipes or drain systems used should be in place to allow over flow during rains to maintain the freeboard. j. the entry pipe should be located above the drain pipe and harvest basin. By having facility to add water above the drain area, you reduce stress on fish during harvest and you keep the fish from swimming out of the lowest area in the pond. (see Figure 3). k. the stand pipe drain should be equipped with a screen having a large surface area to allow over flow of water without loss of fish. Stand pipes are usually of PVC and have an elbow that swivels in the pond bottom at the point where the drain pipe goes through the dike. Thus stand pipes can be “tilted down” to allow water to flow out of the pond. l. drain pipes under the dike require “anti seep collars” of concrete to avoid seepage along the smooth PVC pipe; these collars also help stabilize the pipe. m. ponds should be fully drainable all year round and should be open to receive sunlight. n. a harvest basin is very useful for efficient harvest of fish. These can best be constructed with cement and bricks inside the pond of dimensions 1.2 m x 3 m x 0.3 m deep (see photo in document). o. in most cases, new ponds should be limed (Agriculture lime -1000 kg/ha) and filled. Fish should be stocked once the soils have become saturated with water….up to one week after filling. p. dikes should be covered with top soil and sown with grass cover to prevent erosion. q. most ponds are rectangular with smaller ponds (100-500 m2) used for holding brood fish and spawning and fry rearing. Fry are often raised in tanks or hapas to 1-3 g size as this reduces predation and increases survival. r. records should be kept of all aspects of pond construction including labour, materials, hire of equipment, etc.