Monday, November 10, 2008

Brood Fish Transport

In India two successful models of closed system live fish carrier tanks have been designed to carry brood fishes. One is due to Mammen (1962b), which is known as “splash less tank”. The latest model of the “splash less tank” is of petrol tanker design of 150l capacity with an auto clave type lid. It has a built in aeration system for supplying compressed air, which works on a belt driven by the engine of the transporting vehicle. An oxygen cylinder is carried only as a stand by emergency. The inside of the tank is lined by U-foam which prevents the physical injury to live fish during transport. A total weight of 250kg brood fish can be transported at a time in “splash less tank” Adult Catla weighing about 60kg has been transported in this tank successfully. Generally one kg fish is transported with 4.5l of water.

The other live fish carrier is designed in India by Patro (1968). Patro’s carrier is of a laboratory gas supply design type and comprising an outer chamber of 120cm dia open from top and slightly smaller inner one closed from top, the later during transport, fits inside the former. The inner chamber is provided with an air vent and an oxygen valve. The outer chamber serves as a storage tank and initially filled with water along with fishes to be transported. The U-foam prevents the fishes from injury during transport. The double barrel sized carrier described by Patro, can transport 100kg of brood fish at a time. The oxygen is supplied in the tank with an interval of 5hrs to keep the fish healthy.

Some chemicals are also used to transportation of live brood fish. The sedatives are used in transportation can decrease the rate of oxygen consumption and reduce the rate of excretion of carbon dioxide, ammonia, and other toxic wastes. It can control the excitability of the fish, thus reducing the chances of injury.

Natural Resources of Seeds:

In early days generally seeds of Indian Major Carps are collected from natural resources for culture in fish farms. The techniques of collection of seeds from natural resources are described bellow.

Site Selection for Collecting Fish Seeds:

Before selecting a suitable site for collection of spawn in a given stretch of river, a pre monsoon survey is generally conducted. The river meandering with oxbow lakes, flooded areas of river banks, shallow areas flooded with rain water are suitable for collection of fish seeds. The bends and curves of various shapes in the river course often show a precipitous, fast eroding bank on one side, called here, ‘erosion zone’ and a flat, gently slopping bank exactly opposite, called ‘shadow zone’. Both these banks are unsuitable for collection of spawns. Better collection sites lie on the side of the slopping bank, but at spot where the current just diverges casting off spawns to the sides, as if by centrifugal force. At such sites, a large number of spawn collection nets are usually be operated.

Gears Used for Collection of Spawns:

The spawns are collected by special type of nets, called shooting nets. This is a funnel shaped, net of finely woven netting and is operated in shallow margins of flooded rivers with mouth of the net facing the current. At the end of the net a bag like structure is attached, called ‘gamcha’ to store the spawn inside of it. After a certain periods of time, the cod the spawns are collected at this cod end. The net is fixed by four bamboo poles, against the current of rivers. Various types and modification of these nets are used in different parts of India. In North-east Bengal, the spawn collection nets are called benchi jal. In South-western part, the nets are called Midnapur type nets.

Methods of Collection:

The shooting nets are fixed in such a way that its axis is in line with current directions. To start with bamboo pole is planted firmly in the selected spot, the loops of one end of the nets mouth slipped over it, the other end is stretched firmly across the path of the current and fixed in place with the help of another bamboo pole. The net is then allowed to drift in the current, mouth facing to the current of water. The net is then stretched firmly along the axis, by pulling the cod end ring which is then fixed in place with the help of more bamboo poles. The anterior end of ‘gamcha’ is then tied round the ring, while the posterior end is fixed in position with the help of two more bamboo poles. In order to prolong the life of the net and ‘gamcha’, they should be invariably pulled out of the water after 12hrs operation and dried for at least 24hrs.

After storing suitable quantity of fish seeds, the tail pieces of nets are removed and the spawns or seeds of fishes are scooped out. The collection of seeds from tail pieces are carried on after an interval of 15min, 30min, 1hrs, or 2 hrs depending on the intensity of the collections. Before scooping, the debris accumulated inside the ‘gamcha’ are removed carefully with expertise hands.

Methods of Measuring the Quantity of Spawns:

The spawn collected is to be measured in 200ml, 100ml, 50ml, 30ml, 20ml, 10ml or 5ml measuring cups, depending upon their bulk. For temporary storage the spawns are stored in hapas, made up with muslin cloth, fixed in the shallow water of river margins or creeks.

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