|Biodiversity in the Western Ghats: An Information Kit (IIRR, 1994, 224 p.)|
Among the 20,000 species of fishes known, more than 2000 are found in India. The country's great river systems and extensive network of irrigation canals, reservoirs, lakes, tanks and ponds are some of the many freshwater ecosystems for fish.
Estuaries, lagoons, backwaters, impoundments, mangroves and swamps harbor a wide variety of estuarine fish. These estuarine ecosystems represent a few of the brackish water ecosystems found on the west coast of India.
The estuaries of west-flowing rivers such as the Zuari and Mandovi (Goa), Netravathi Gurupur (South Canara) and Kalinadi, Aghanashini and Sharavati (North Canara) provide excellent habitats for fish.
All the rivers of the west coast of peninsular India arise in the Western Ghats hills and flow for a short distance into the Arabian Sea. Though many are perennial, others are torrential streams only during the southwest monsoon. The major fishes of these rivers include carps, catfishes, mahaseers, mullets, perches, and pearl spots.
Fish like the Indian shad, Hilsa ilisha, which migrate into rivers from the sea for spawning are called anadromous fish. Local fish that migrate between ecosystems in search of breeding grounds include the mahseers, the Indian major carps and large and medium-sized catfish.
Types of fisheries
Two types of fisheries are found on the west coast of India:
· Capture fisheries-In the sea, rivers, estuaries, large reservoirs, and lakes. Here, people reap without having to sow. Fish stocks are replenished naturally.
· Culture fisheries-Otherwise known as pisciculture, culture fisheries are done in small water bodies which people can manipulate. The fish fry have to be sown, tended, nursed, reared and finally harvested when grown to table size.
Important fishing gear used in West Coast includes shore seines, gill nets, cast nets, hook-and line nets and mini-otter trawls.
What are fish?
· Are cold-blooded
· Have a backbone
· Live in water
· Breath with gills
· Use fins to balance and move
· Most have scales.
Fish are classified into two major groups:
· Bony fish (e.g., carp, mullets)-skeleton is of hard bones.
· Cartilaginous fish (e.g., sharks, rays)-skeleton is of soft and flexible cartilages only.
Types of fisheries
Endemic and exotic species
The following fish are endemic to Western Ghats river systems.
· Mahseers (for spp)-One of the most important game fishes of India. (Tata Electric Company has developed ways to restore and rehabilitate them in Lonawala and Koyna water reservoirs)
· Tor khudree (Khudree Mahseer)-Attains a length of 1.5 m, found in Walwhan and Shirawta reservoirs of Lonawala, streams of South Canara and down to north Kerala.
· Barilius bendelisis-An important game fish found in Nilgiri waters.
· B. gatensis-Attains a length of 150 mm. Found in the streams of the Western Ghats.
These cultivable fishes are extensively used in intensive freshwater aquaculture.
· Grass carp (Ctenopharyngodon idella)-Introduced from Japan in 1959 for experimental culture and weed control.
· Silver carp (Hypophthalmichthys molitrix)-introduced to India from Hong Kong in 1959 for experimental culture.
· Tilapia (Tilapia mossambica)-introduced from Bangkok in 1952 for experimental culture. Original inhabitant of rivers of East Africa.
Burden of fatherhood
Some male fishes "deliver" their young. Male tilapia (Tilapia mossambica) pick up fertilized eggs, incubate them in their mouths, and deliver the young ones. This is known as buccal incubation and is a kind of parental care. This behaviour ensures greater survival of young ones.
Some catfishes also take care of their young in this way.
The paternal brood pouch of a male sea horse (Hippo campus) enables its young to pass their embryonic days inside their father. Later, he "delivers" the young ones.
Uses of fish
Food-High nutritive value, contains protein (about 20%). Fish oil has higher proportion of unsaturated fatty acids. Fish is a good source of trace elements like Cu. P. Fe and I, and of vitamins A and D.
Economy-Sustainable fishing generates economic prosperity. Fish bones are used to make combs. Shark skin is used to make high-quality leather purses, belts and shoes.
Organic manure-Non-consumable fish is used in agriculture as organic fertilizer as it is rich in nitrogen and phosphates.
Medicine-Unsaturated fatty acids in fish oil are good for the heart. They also prevent cellular aging and are used to make gelatin. Fish oil (such as shark liver oil) is used as therapeutic agents for vitamin A and D deficiencies.
Animal and poultry feed-Fish meal is used to feed ruminants and poultry. It increases milk supply and weight gain.
Pest control-Gambusia sp. (common guppy) is used to control mosquito larvae. Grass carp is used to control aquatic weeds.
Education, research and recreation-Fish have many uses for teaching and research, and for aesthetic reasons (e.g., aquarium fishes).
Some economically important fishes of the West Coast
Anadostoma chacunda llisha indica
Mugil sp. (mullet)
Cyanoglossus sp. (sole fish)
Tachysurus sp. (marine catfish)
Pseudorhombus triocellatus (flounder)
Kowala coval (sardine)
Sphyraena sp. (barracuda)
Rastrelliger kanagurta (Indian mackerel)
Etroplus suretensis (pearl spot)
Indian major carps
· Catla (Catla catla)
· Mrigal (Cirrhinus mrigala)
· Rohu (Labeo rohita)
· Calabasu (Labeo calabasu)
· Common carp (Cyprinus carpio)
· Implement existing mesh size limits (the minimum mesh size for nets is 30mm)
· Implement size limits to allow juveniles to reach maturity.
· Enforce a closed season ban on fishing during June-July to September, so that fishes can spawn and breed.
· Prevent pollution: Prevent domestic sewage and industrial effluents from entering the breeding zones of fishes in rivers, estuaries and seas.
· Declare sanctuaries: Major breeding zones should be declared as sanctuaries.
Air breathing fishes
Some fishes are provided with accessory respiratory organs which enable them to live out of water for a long time. They include:
Mystus seenghala (freshwater catfish)
Clarius batrachus (catfish)
Boleophthalmus sp. (mud-skippers)
Periophthalmus sp. (mud-skippers)
Anabas testudineus (climbing perch)
Channa punctatus (snakehead)
Heteropneustes fossilis (stinging catfish)
Rasbora daniconius (danio)
Glossogobius giuris (goby)
Water balance (osmoregulation) in fishes
Since the liquids in a freshwater fish's body are saltier than the surrounding water, it is in constant danger of soaking up water and swelling, just as a bladder of salt water in a laboratory beaker of fresh water. As a result, it doesn't drink, and what water comes in through the skin and gills is carried to the kidneys and used to carry away waste products in large quantities of urine.
A saltwater fish has exactly the opposite problem. Its liquids are less salty than the surrounding water, and it is in constant danger of dehydration, like a shrinking bladder of fresh water in a laboratory beaker of salt water. Thus the fish must drink large quantities of water to make up for what it loses through its gills and skin. Some of the salt goes through the digestive tract and is excreted. Some is forced through special gill cells back into the ocean. A saltwater fish seldom urinates.
Prepared by Dr. A. Thomson Mathai