The place in where particular plants or animals live is known as habitat. Within the habitat, organism occupies different niches. A niche is the functional role of a species in a community. Habitat is a place where species get what they need to survive food, water, cover, and a place to rare young. Habitat improvement refers any kind of positive changes in the habitat, which provide favorable condition for growth, and maintenance of life is called habitat improvement. On the other hands habitat improvement is defined as a fisheries management tool. Habitat improvement is done to provide better environment condition for desired species and to get maximum sustainable yield per unit area.
The fish species present in lentic water bodies are influenced by natural migration, transfer by animals or men. Although some of the methods can apply both in still or running water, but these different habitats normally require separate tactics. However, the following methods can apply in still or lentic water bodies.
A) Physical improvements
B) Chemical improvements
C) Biological improvements
A. Physical improvements
The physical improvement of the habitat of still waters has received much attention in the USA and is gaining popularity in European fisheries, especially in Austria, Switzerland and South Germany. A wide variety of management techniques are followed during physical improvement. Some of the physical improvement includes providing area and shelter for desired species, ensures available slight, provide spawning facilities and control of turbidity. The important physical improvements are as follows–
i) Provide cover and shelter: It has important on fish habitat improvement. Bamboo poles or branches of tree without leaves are used in these purposes. Tying bushes together and weighting them so that they sink can make brushwood reefs. More recently, reefs of old car and lorry tires have been used effectively for the same purposes. These are inert, do not rust or cored, and will not contaminate the water. Polypropylene or nylon rope is used to develop the structures together and can be used for these purposes. Cover and shelter is provided for the development of feeding ground, make spawning and nursing ground and sometimes substrate are used to remove ectoparasite.
ii) Ensure adequate light: Adequate light ensures the optimum range of primary productivity through photosynthesis and play important role in providing sufficient food for all aquatic organisms. Producing of fish food, reproduction and other biological activities are hampered due to lack of sufficient light penetration into the water body. Excess light may cause sunburn on the head as well as body surface of fish. To maintain the available light following steps can be taken-
- Big shady trees on the embankment especially on the east and the west sides of the water body should be removed.
- Controlling the excess aquatic weeds.
iii) Control of turbidity: Turbidity is defined as the amount of dissolved and suspended matters in water. Turbidity 20000 ppm or more considered lethal to fishes (Irwin, 1945). Through the turbidity caused by plankton is desirable for fish but the turbidity due to surface run off, colloid, clay and other soil particles limit primary productivity by a thin surface layer and causes many problems especially respiratory problem to fishes and other physical injuries. Turbidity can be controlled by the following methods-
- Raising embankment can control turbidity due to surface run-off that occurs in rainy season.
- Turbidity caused by colloids, clay and other soil particles can be controlled by chemical treatment. Aluminum potassium sulphate: 20-60 kg/acre, Hydrate lime: 150-200 kg/acre, Agricultural gypsum: 150-200 kg/acre are used as chemical treatment.
- Turbidity caused by some species e.g. Carpio, in this case, reduction or elimination of such species can be done.
- Turbidity because of bottom clay can be removed by spreading sand layer on the whole pond bottom.
- Turbidity due wave action by using bamboo poles lying over the water body.
iv) Provides spawning facilities: In present, most of the natural spawning grounds are almost destroyed. Moreover, the demand of fry and fingerlings is increasing day by day. Physical method of habitat improvement provides spawning sites and areas. Creating of space, place, and condition for the spawners can be done in the following ways-
- Increasing littoral zone especially for small fishes.
- Facilities can be provided for nesting or breeding places of the desirable species.
- Hard bottom should be kept especially for shell fishes e.g. prawn, shrimp, crab
B. Chemical improvements
The chemical nature of the water in a fishery is important as it often determines the biological productivity of the water body. The important chemical improvement techniques are as follows-
i) Liming: Lime is used as chemical substance which improves the aquatic environment. Lime is in three forms such as lime stone (CaCo3) in powdered condition, hydrated lime [Ca (OH) 2] and quick lime (CaO). In order to increase the productivity of an established pond, it is often necessary to raise the pH of the pond soil to promote primary productivity. Results of liming are as follows-
- It raises the alkalinity, hardness and pH of a pond.
- It makes the carbon-buffer system stronger.
- Reduce turbidity.
- Act as an antidote.
- Removes humic acid.
- Destroy pathogens and parasites.
ii) Fertilization: Through fertilization, nutrients are supplied to a water body to increase primary productivity that makes the population density of phytoplankton, zooplankton, benthos and other fish food organisms higher and higher fish food organisms increased fish yield manifold.
Doses of fertilization: Fertilization should be done carefully with effective doses considering the prevailing physico-chemical and biological condition of water body. When transparency of water is less than 40 cm then no fertilizer should be applied, transparency within 40-60 cm then routine fertilization necessary and transparency up to 60 cm then routine fertilization is necessary if possible over doses may consider.
iii) Ensure regular supply of oxygen: Regular supply of dissolved oxygen is required by all the aquatic organisms (except of anaerobic bacteria) for growth. An amount of 5 ppm or more dissolved oxygen is suitable for aquatic organism. If dissolved oxygen insufficient for a long time then organism may be infected by various bacteria and other diseases, fishes become physiologically weak and may cause fish mortality. So, in a culture pond the normal required amount of dissolved oxygen should be maintained through scientific management for high producing of fish production. Oxygen is important for respiration of organisms and decomposition of dead organic matter. The standard level of DO is 5 ppm. The steps that are taken to increase DO in the water body are as follows-
- Agitate water surface of a pond with bamboo poles
- Swimming with precautions for availing turbidity
- Aerate water through different types of aerator
- Stopping fertilizer incase of heavy phytoplankton bloom
- Pond water may be replaced by oxygenated water
- Potassium permanganate (1-3 ppm) may be sprayed
iv) Control of pollution: Pollution is one of the most important factors of habitat improvement in standing water body. Pollution increases osmotic pressure, temperature and hardness in water and it decreases oxygen level, hinders physiological function of aquatic animals and causes scarcity of food. Fish and shellfish harvested from polluted waters may be unsafe to eat.
Control measures against pollution:
- Industrial waste should not through indiscriminately. It should be pre-treatment plant before throwing to open water.
- Use of pesticides and herbicides should be limited.
- Excess use of fertilizer should be prohibited.
- Water inlet from the cities must have to be treated before entering into water.
- Various mineral substances keep away from water.
- Domestic wastages should not throw in the water.
- Sanitation must be introduced.
C. Biological improvement
The physical and chemical improvement in still water may produce a measurable improvement for the fish at present. It is also possible assist this habitat improvement process by the deliberate addition of fresh water plants by other biological means. Following ways- does biological improvement
i) Aquatic vegetation: Aquatic vegetation is considered as a natural habitat, because growth of aquatic vegetation occurs in a man-made impoundment by natural means. Aquatic vegetation may be transported through drift from feeder streams in the watershed. Throwing them or dropping them into the water at the required place generally plants submerged or floating plants. By this process water body is benefited by-
- Oxygenation due to photosynthesis activities
- Act as a shelter and protect from predators
- Act as a breeding place for some species
- Plant roots protect soil erosion
- Provides food directly to some species
ii) Population control: A water body may be over populated by under fishing, absence of predation, continuous recruitment and breeding. Population can be controlled by releasing specific predators, reducing breeding propagation, increasing fishing pressure, liberalize fishing, discarded breeding places, selective fishing and angling.
iii) Reduction of predation and competition: Competition and predation ay be occurred within the same species or within the different species. Fish compete for food, shelter and breeding. Predators are bird, mammals, invertebrates etc. Reduction of predation and competition can be done by-
- Netting to eliminate of desired species.
- Releasing of specific predators to remove undesirable species.
- Zonation of the habitat so that species find enough space for food, shelter and breeding.
iv) Control of phytoplankton bloom: Phytoplankton is generally desirable in fish production but heavy bloom makes hazardous to lethal condition for fish and aquatic animals. Phytoplankton bloom can be controlled by following ways-
- Bloom caused due to over doses of fertilization then applying fertilization should be stopped immediately.
- Bloom caused due to input of nutrients are- inlet, sewage inflow, industrial pollution and run-off from agricultural land which is getting regular fertilizer application.
- Excess supplementary feed should be stopped.
- Copper sulfate, simazine and diuron can be used to control phytoplankton as a chemical treatment.
v) Control of parasites or disease: Parasites or diseases hamper the fish growth, cause fish mortality and make the environment inhabitable. It can be controlled by improving good environment and applying control measure treatment. Potassium permanganate (0.5 g/100 litre water) and benzalconium chloride is used as a chemical treatment.
Arrignon J (1900) Management of fresh water fisheries, Oxford and IBH publishing Co. Pvt. Ltd. Calcutta, pp. 199-213.
FAO (1997) Management of fresh water fish culture, Oxford and IBH publishing Co. Pvt. Ltd. Calcutta, 233 pp.
Firehock K and J Doherty (1995) A Citizen’s Streambank Restoration Handbook, Izaak walton League.
Gough S, “Tree Revetments for Streambank Stabilization,” Missouri Department of
Conservation, Fisheries Division.
USDA, Natural Resource Conservation Service (1996) “Streambank and Shoreline Protection”, Engineering Field Handbook, Chapter 16.
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