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 growout. 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, broodstock conditioning, nursery, growout, 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.
Construction of the dikes is one of the most important tasks in the fish or shrimp farm construction process. Slopes are normally set at 2:1, but a wide range of slope ratios have been used over the years. Proper soil compaction and sufficient clay content are very important to maintaining the slope of the dike during the actual operations in the years ahead. The top of the dike is usually made wide enough to facilitate truck movement. Wherever possible, dikes are shared between ponds to reduce earth movement costs. In areas of low elevation that are at risk of flooding or storm surge, a high elevation farm perimeter levee should be specified.
After the pond bottom and dikes are completed, the inlet and outlet structures are constructed. These water movement structures are sometimes referred to as monks. The monks are used to control the amount of water coming in and going out of the pond. In modern aquaculture engineering, monk inlet and outlet structures are usually constructed of formed and poured concrete. There are many different styles and installation points for monks. Our preference is to locate outlet monks in the center of the short side and build them directly into the dike for easy access. Reinforcing steel is used to frame the structural dimensions of the monk. The floor is poured and leveled to the correct slope. Boards are used to shape and level the concrete during the pour. Grooves created in the floor and sides of the monk and the grooves will be fitted later with boards that will be used to control the flow of water in and out of the pond. Some of the vertical space is also fitted with filters to prevent the entry of predators and the escape of the cultured crop. Concrete pipe of the proper diameter is laid on the floor. The entire monk box is framed around this pipe. The size of these structures varies with the size of the pond and with the amount of water that needs to be moved in or out of the pond. In some cases, these structures are used to concentrate the animals for harvest. This is especially true in shrimp farming. A recessed area in the monk box is constructed to give a point where mechanized harvests can take place.
Obtaining the proper grade and slope of the pond bottom is extremely important. If done properly, the ponds will drain completely and can be harvested quickly and efficiently and the pond bottoms can prepared in between crops with much greater ease and efficiency. In areas that have changes in elevation, some pond bottoms may require considerable cutting while others may require very little bottom cut. The overall goal is to develop an entire farming system that is capable of filling and draining using the natural gravitational forces of moving water.