Tuesday, 3 February 2015

FISH FARM DESIGN

Since ancient times, fish have been held in a wide variety of man-made structures. These structures were built using simple methods and readily available materials. The fish or other aquatic crop were cared for by the fish farmer and relied upon as an important source of protein for their families. The typical fish farm was developed by forming small ponds by hand, or an even simpler method of trapping tidal water flow in estuaries by building simple water retaining structures. In less developed parts of the world today, the basic earthen pond design system is still the most important and affordable type of design. Not surprisingly, there have been considerable technical advances over the last few decades that have transformed the aquaculture industry, yet the basic earthen pond system remains mostly unchanged and still highly relevant in less developed countries. The size of earthen ponds built today can vary anywhere from 20 square meters to 20 hectares (44 acres) or more. Pond size is determined by the type of species cultured, the intensity of the system, size and maturity of the species being farmed, access to capital, land availability, water availability, the harvesting method, and even the marketing and sales goals of the project. The species being farmed and the size of animal as it grows through various stages of development plays a big role in pond size and farm design. For example, a commercially oriented tilapia farming operation typically utilizes 0.1 or 0.2 hectare ponds for nursery phases and 0.3 to 0.5 hectare ponds for grow out. Semi-intensive shrimp farms generally use 7 to 20 hectare ponds, while more intensive shrimp farms generally use ponds less than 7 hectares and quite often less than 1-2 hectares in size. Most ponds are rectangular in shape, but there are also square, circular, and irregularly shaped ponds in existence. Most farms build the ponds to maintain a minimum water depth of at least 1 meter with levels of around 1.5 meters considered ideal. Ponds are also used for many different purposes: spawning, brood stock conditioning, nursery, grow out, or finishing. Quite often, the expected use of the pond dictates the design. Once a high potential site has been thoroughly analyzed and found suitable for fish farming or shrimp farming, it must be surveyed. Based on this detailed survey and the targeted production strategy, farm design plans are then drawn up by an experienced aquaculture engineer and the project manager. The possible ways to design a farm are endless, but certain designs are definitely more efficient and effective than others. Farm design is always an exciting period, but it takes a skilled and experienced aquaculture engineer to put together the best shrimp or fish farm design for a given site. It may look easy, but it is really a very involved and complicated process. Once detailed aquaculture engineering designs and drawing are in place, the actual construction of the farm can begin. The slope of a pond is always less than 1% and usually closer to 0.1%, particularly when the pond is large. Cut and fill volumes are determined from the topographic survey of the area and equipment operators are guided by elevation stakes set on-site. Earth movement is ideally accomplished using tractor drawn scrapers, but the use of bulldozers is the more common method. Tractor drawn scrapers that are guided by lasers can give a perfect slope and high rate of compaction, resulting in a perfectly constructed pond under ideal soil conditions. This kind of equipment is expensive and not always available, but it is our strong recommendation to use this method of shrimp and fish pond construction whenever possible, especially on larger projects where the purchase of new or used earth movement machinery is warranted.

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