It is not an irony that water is the most abundant resource yet limited in supply. According to statistics, Earth mainly consists of water. Around 71 percent of the Earth surface is made up of water, and oceans account for about 96.5 percent of all Earth’s water. It can be deduced from above that less than 3.5 percent of total surface water is fresh enough for fresh water fish production. As a matter of fact, fresh water is everything in both natural and artificial fish production. Among three important factors of catfish production (Breed, Feed and Water), water is most important. The reason for this is not far-fetched. Catfish live, feed, breathe, reproduce and exist in fresh water environment only.
Due to limited supply of fresh water, and for the fact that fresh water is not evenly distributed (both ground and surface water), there is need to manage this scarce resource well. A catfish farmer, whose business is water based, must learn the art and science of water management techniques that suit his budget and environment. To this end, various water management systems with their merits and demerits are discussed in this article.
Common Water Management Systems in Aquaculture
There are at least three kinds of water management system available for catfish farming namely;
- Re-circulatory System
- Flow-through System
- Stagnant-pond System
Re-circulatory system, in catfish production, is made up of close or partially-close system of indoor water management techniques where used water is treated for re-use in catfish farming. Used water is treated for chemical, gaseous, biological and solid waste before re-use. Water is treated by different techniques and equipments to ensure healthy aquatic environment for catfish production. Also, the system controls pH and water temperature to ensure a conducive environment for fish growth. Generally, re-circulatory system is made up of fish maintenance tank and composite system. A complete re-circulatory system may comprise the following; Tank, screen/sand filter, filters, aerators/oxygen pumping machine, submerged heater/chillers/heat exchanger, linking pipes.
Merits of Re-circulatory System
- It promotes efficiency of water management by ensuring limited water resource is judiciously used.
- It ensures economy of land because of its high density stocking capability.
- It is environmental-friendly. Used water is treated before being released into the environment.
- Controlled production environment reduce to barest minimum certain infections.
- Encourages mass production of catfish per area of land.
- Increases survival rate and ensures low mortality due to reduced risk of diseases.
- Stable environment for optimal growth.
De-merit of Re-circulatory System
- Expensive to set up.
- High cost of maintenance.
- Can only be handled by trained manpower.
- High cost of operation.
- Breakdown in any part of the system will affect the entire system.
- Cannot be operated in absence of electricity.
Flow- through System is water management system in fish farming in which water is allowed into the pond through an inlet pipe(s) and used water is released into water body to keep the pond refreshed. Sometimes, water coming into the pond may be treated or may not be treated. The main reason for setting up this system is to limit water pollution and its effects. Where there is no much water, used water from the ponds is re-used by allowing it to settle down in settlement dam/tank. Flow-through system could be intensive, semi-intensive or extensive system. Pond operating flow-through system is carefully constructed in such a way that fresh water is allowed into the pond either through pipe network or concrete raceway. In earthen ponds, flow-through system can be operated manually by linking the source of water (stream, river, dam, etc.) to a receiving pond from where other ponds get their share of water. The used water is released through the last pond in the row. However, this might not be feasible in concrete ponds. Most often, source of water to concrete pond is mostly higher than the level of the pond. This will enable water to flow from the source into the pond without any aid of electricity.
Merit of Flow-through System
- Simple to set up.
- Low setup cost.
- Easy to maintain.
- Low cost of maintenance.
- May not need electricity to operate.
- Can be handled by people of little or no training.
Demerit of Flow-through System
- Can only be efficient where water is available in good quantity.
- Where inlet water is not treated, infection can find its way to the pond.
- Not effective in dry season.
- Water can be polluted through the supplying source.
- Pipes can be blocked by unscreened particles.
- It could be at the risk of flood when inflow of water is not controlled during rain.
- Temperature of the pond depends on environment condition.
Pond/Stand-Still System is a static system of water management where pond water is rarely refreshed through external source. It is often used where there is no stable surface water to refresh the pond. However, farmer must be sure of the water retention ability of such an area. After pond preparation, pond is filled with water either mechanically or naturally recharged through ground water for production of fish for a season. Ponds under this system are under-stocked or moderately stocked to ensure fishes are raised for the whole season without much water management challenges. At the time of harvest, pond water may be completely drained by the use of pumping machine or lease pipe. Where farmer is not sure of the recharging power of the ground water, pond is poisoned to retain the water for another season production.
Merit of Pond System of Water Management
- Less expensive to maintain.
- Less likely to be affected by external disease/ infection.
- Easy to manage and maintain.
- Less likely to be affected by flood.
- Can be used in absence of surface water.
Demerit of Pond System of Water Management
- Cannot be used for high density production.
- The whole stock can be lost in case of disease outbreak.
- When moderately/overstocked, fishes may not attain their growth potential.
- Large space of land is required for production.