Department of Fishery, Kirtipur, Kathmandu, Nepal
ABSTRACT
Mahseers (Tor tor and Tor putitora) have a potential for being ranched in rivers/artificial channels of Nepal and other countries of the Trans-Himalayan region. This is one of the hopes for rehabilitating mahseer stocks in rivers and to enhance them to a sustainable fishing level. It is proposed to spawn mahseer in artificial channels alongside streams and rivers, to be followed by releases of fry and fingerlings into streams and rivers for their downstream migration and feeding in the lower reaches of rivers. Protection of growing fish will be essential, especially of the mature stocks migrating upstream for breeding.
The mahseers (Tor tor and Tor putitora) are superior game fish of the cold water streams of Nepal. Few fishes of the mountain stream illustrate vagaries of human taste better than the mahseer. Their sporting attributes plus good public image provide a background for expanding recreational fisheries in the Himalayan waters. The mahseer fishery has declined much owing to ecological changes in waterways brought about by barrier effects of dams, inroads of pollution and harmful fishing practices. At many places river courses have changed and spawning beds were destroyed. Destruction of spawning beds and resultant failure of spawning affected seed and fry resources greatly. If the natural spawning of mahseers goes unmonitored, the valuable mahseer fishery resource of Nepal will become extinct. Mahseers do not breed in a closed system of impoundments although they can grow to maturity there. They need free-flowing turbulent water fed by melting snow. Their spawning beds must have good-sized pools and rapids, sand bars and gravel. In a closed system of pond water, all these basic habitat needs are not met; therefore, mahseers refuse to breed. In many pristine rivers of Nepal, spawning beds are destroyed by dams which can never be compensated. To evolve the original spawning beds takes a long time. But a new spawning channel or incubation channel can be created by habitat manipulation, which can be done by diverting an original river course or side channel at a desirable spot. In rivers of Nepal, such ideal channels are many and can be utilized with little effort. The channel so created may act as fish sanctuary or buffer zone or escape area and help to conserve upstream migrating spawners year after year. Along the diversion side, a river can be tamed so as to create a full-fledged riverine fish farm, where migratory stock of mahseer can be regularly ranched. This will greatly help to conserve fish seed resources and bring back depleted fish stocks to the original level of abundance.
The mahseers have complete freedom to migrate to and from feeding and breeding grounds. The improvement over nature is obtained by artificially incubating and hatching eggs of the fish, as rearing the young is the greatest natural loss in the wild. It must not be confused with what is called enhancement. This means releasing eggs, fry and fingerlings of fish in sections of river or reservoir which the adult fish cannot reach on their spawning migration or which are unsuitable spawning grounds, but can provide useful rearing areas for young fish. The development of artificial spawning channels for migratory fish is a half-way stage between full ranching and enhancement. Gadkhar creek, joining the Tadi River, serves as a natural spawning creek. A typical spawning channel is an artificial channel made beside a natural river, or across the loop of a wide bend. The bed of the channel is covered by graded gravel of correct size to be used as spawning substrate by fish. The inflow and outflow of water are controlled by sluices and valves and the length of the channel may be divided by screens or weirs. Adult fish returning into the channel spawn there naturally. Alternatively, fish can be stripped and fertilized eggs deposited in an artificial nest or gravel incubator. The method is of real value only for species which migrate downstream as fry. If the young fish have to be fed artificially for a longer period, it is better and more easily done in tanks with free flowing water through a cascade system. The ranched mahseer therefore have complete freedom to migrate to and from large river to creek, i.e. from feeding grounds to spawning grounds, and vice versa. The improvement over nature is made by artificially incubating and hatching eggs and rearing. In the USA the use of spawning channels has increased harvest of Pacific salmon. This method is to be tested on mahseer migrating from a river to creek and vice versa. In the incubation channel young fish can be fed, but this is better and more easily done in tanks.
2.1 Open water - artificial river
The artificial river made near a natural river course or incubation channel meets all habitat needs and has an advantage over the traditional "Put" and "Take" systems. In this system, spawners are encouraged to use the spawning channel and some of them are subjected to captive breeding and rearing experiments. Hatchery-bred fry could be stocked and raised to fingerling stage on a mass scale and released back into the river. This will rebuild fish population in the river and counteract forces of overfishing. In other words, this new system is called an open water "Raise and Release" system, as this system enhances controlled breeding of fishes and helps to preserve gene pools of rare stock of the Himalayan fish.
2.2 Difference between mahseer ranching and farming
In fish ranching, as opposed to farming, fish are kept in captivity during the early stages of their life. When bigger they are allowed to spend life as free ranging animals. Mahseers, which spawn in hill-streams and brooks, but spend most of the later part of their lives in large rivers, are well suited for fish culture. In culture the mahseer Tor putitora can be hatched and confined until it reaches advanced fingerling stage (about one year old), at which time it should be released for the journey to the rivers where it will stay and grow to maturity, to return to the historical spawning beds to spawn. Mahseer ranching differs from actual fish farming in several ways. While farming involves cultivation of many species, commercial fish ranching has so far been broadly successful with single or monospecies of migratory fish only. This does not rule out the commercial possibility of ranching free ranging river carps. So far they have not been ranched and the ranching potential has not been tried. The second main difference lies in feeding, i.e. farmers must provide all food for fish they rear, either directly or indirectly. This is not the case with mahseer. The present investigator has estimated that 1% of mahseer growth occurs while it is in the hatchery. For the two, three or four years in the large river, the mahseers forage on their own.
2.3 Dynamics of the mahseer ranching
Many feeder streams and rivers joining the Trishuli River have spawning grounds. Spawning beds of the Tadi River located near the Gadkhar fish farm may be selected for mahseer ranching. This area is ideal because traditional mahseer stocking ponds are located very near to the Tadi and its feeder stream, Khahare Khola. The confluence of the Tadi and Khahare Khola is an ideal site for collection of migrating spawners which were used by us as spawners. In the entire stretch of the Khahare Khola up to 3 kms upstream are ideal environmental conditions for mahseer spawning: gravel beds, suitable water current, high dissolved oxygen content, good water quality. If this stream is changed into artificial mahseer running channel in conjunction with an existing fish farm, it would certainly help the mass production of mahseer in semi-natural conditions. Mahseer ranching would represent a visible step in transition from a hunting to farming economy in the Himalayan waters of Nepal. In an open water system much depends upon the hydrological regime of the mountain river, such as flood and drought. The changing river conditions affect abundance of mahseer. Seasonal variations lie beyond the control of man, but can be manipulated to some extent. Other factors are however within our power. The basic content of mahseer ranching is that the mahseer population of each river and feeder stream must be treated as a separate breeding unit and for each a sufficient number of adults must be allowed to escape fishery and spawn in clear, undamaged environment. If this is done, strong migration may become an annual phenomenon, perhaps exceeding the runs of the past.
2.4 Rivers suitable for ranching
It is a waste of time and money to try to start ranching in an area where there is an intensive fishery. The mahseer need a clear run home for their riverine feeding grounds, without being captured on their way. There are not many places such as Gadkhar fish farm where ranching is possible. It is quite possible to induce the return of mahseer to a small creek near the farm, where produced fish will return to a small shallow area where they can be captured easily. Small creeks can be made attractive to river running mahseer, and entry can be facilitated by artificial spates created by releases from a low stone dam.
2.5 Basic analogy between salmon and mahseer
Mahseer ranching can be achieved by stocking fingerlings in natural water in the same manner as has been done in case of the salmon in the U.S.A. Salmon hatcheries in the U.S.A. are established near dams where ripe male and female salmon trying to migrate upstream are stripped, egged, and fertilized and hatched, and the resultant fingerlings released downstream to go to sea, grow and migrate back again to serve as commercial stock and also spawn into a new generation of salmon. Likewise, the migratory male and female mahseers could be collected at the confluence of river and stream, stripped, fertilized, and egg-reared to fingerling stage in specially designed riverside hatcheries fed with river water. The fingerlings so produced would be released back into the river to grow further and come back to spawn in the stream where they were born. Experience of the past decades within traditional ponds of Nepal has shown that female mahseers grow to maturity in the stagnant water of a pond, but do not develop their gonads and spawn there. The sexually ripe female with running ovaries, if put in a pond for breeding, absorbs ripe eggs within a few days. Male mahseers are known to mature in impoundments and produce milt and would be useful as standby stock or a milt-bank. The one would need to capture only the females on their spawning grounds of the river. In the United States, salmon ranching has been carried out with great success (Bakkala, 1964; Lucas, 1960; Mackinnon, 1960; McNeil and Baily, 1975; Shrestha, 1986; and Thomas and Shelton, 1969).
2.6 Transition to mahseer hunting and farming economy
A mahseer ranching programme is based on the homing instinct of this fish. Like the salmon, mahseers when released in an unnatural setting, manage to find their way back home years later at the time of breeding. Such unerring homing instinct ensures the mahseer return to their birth place; they are therefore exceedingly easy to harvest when they arrive. In order for mahseer ranching to succeed, enough mahseer must survive to return to point of release, at a spot where they can be captured on a profitable scale. The possibility of raising mahseer in cages and raceways suspended in a reservoir or lake is still to be assessed.
The attraction of Himalayan mahseer ranching is that the investment in feed is limited to one or two seasons; mahseer need to be fed between the time of hatching and the point when tiny fingerlings or smolts are ready for their long feeding migration to the river. Feeding strategy of the mahseer during the course of its river migrations depends on the water quality and other factors, such as temperature, photoperiod, rainfall, presence of prey organisms. During its up river and down river migrations in June-October it feeds on zooplankton, fish fry and larger fish, crabs and molluscs. The mahseer heading towards itsspawning creek may have a long journey from the large river. This is an important consideration in ranching because the fish will be in better condition if it has a short return migration.
Ranching mahseer by taking advantage of the growth of the fish in the open water of a large river, is an attractive proposition, and one of the most exciting possibilities of mahseer farming in the various open waters of the Himalaya. The future success of any kind of ranching and the status of the natural stock of river-going mahseer each year depends upon the cooperation of fishermen, anglers and national conservation agencies.
An imaginative design of mahseer running ranch-cum-fish farm would be welcomed by cold water aquaculturists in the countries of the Trans-Himalayan region and some adjacent countries as well.. Establishment of mahseer ranches at suitable places alongside rivers would help not only to enhancce its production, but also to save its dwindling stocks, preserving gene pools for posterity.
References
Bakkala, R., 1964. Abernathy, spawning channel proves effective for reproduction of chum salmon. U.S. Bureau of Commercial Fisheries Review 26(12): 20-21.
Lucas, K.C., 1960. The Robertson creek spawning channel. Canadian Fish Culturist No. 27: 3-23.
MacKinnon, D., 1960. A successful transplant of salmon eggs in the Robertson creek spawning channel. Canadian Fish Culturist No. 27: 25-31.
McNeil, W. J. and J.E. Baily, 1975. Salmon Ranchers Manual. N.W. Fisheries Centre, Aulk Bay Fisheries Laboratory Publication.
Shrestha T.K., 1986. Artificial Himalayan Salmon spawning. Tribhuvan University, Kirtipur Campus, Kathmandu, Nepal.
Thomas, A.E. and J.N. Shelton, 1969. Operation of Abernathy channel for incubation of salmon eggs. U.S. Fish and Wildlife, Bureau of Sport Fisheries and Wildlife. Technical Paper No. 23, pp. 1-19.
