6.1 Maintenance of Fingerling Stocks
A critical factor for the development and expansion of cagefish culture will be the timely availability of adequate fish fingerlings.
The Fishery Development Centre must make the necessary arrangements to keep adequate stocks of fingerlings. The Bhairawa Fishery Centre has been expanded and provided with adequate facilities so that it could supply Pokhara with the needed fingerlings.
The six ponds, totalling about 0.35 ha, have been reconstructed and they could be fully utilized for rearing small fingerlings brought from Bhairawa (or other centres). When they reach an average size of 10–20 g they could be transferred to floating cages with small mesh. Cages for these have already been made and more could be made as required.
These nursery cages need to be located where adequate plankton is available. Of the three lakes Rupa Lake is the best, next comes Begnas Lake. In Phewa Lake they could be located in Khapaudi or on the deep trench where zooplankton is abundant. Grass carp have to be regularly fed with grass or other fodder. A watchman for each lake may have to be provided, where necessary.
Advantages of raising fingerlings beyond 10 g in nurseries rather than the project ponds are as follows: mortalities are likely to be less; a more accurate estimate of available stock sizes is possible from floating nurseries, where mortalities can be monitored more precisely, and they can be stocked more heavily than ponds. When fingerlings raised in cages are stocked in other cages they are already used to cage life and mortalities as a result of attempting to escape from the cages, handling, etc., will be less.
The project nursery ponds should be used as many times as possible per breeding season to produce fingerlings from fry.
6.2 Maintenance of Records
The development and expansion of cagefish culture in the private sector will depend to a large extent on the extension services provided by the technical staff of the Fishery Development Centre.
It would be advisable to continue the practice of maintaining a file for each cage-fish farmer and to record relevant data, according to species and dates, such as stocking numbers, mortality and the causes, removal or sale of fish, settlement of loans, maintenance work on cages and other expenses. This should be continued at least till the loan on each initial cage is settled. This would involve regular visits to the cages and assisting the farmers in all aspects of their fish culture work, including the maintenance of their accounts.
6.3 Distribution and Cages
With regard to type and number of cages, a variety has been demonstrated, and the farmer could use the types of cages he prefers. For a start, it would be advisable for the Fishery Development Centre to give out at least one cage to each applicant and provide more as he gains experience and shows evidence of success. However, a prospective farmer wishing to provide himself with his own cages, could also be encouraged to carry out fish culture in the lakes. The interests of the poor fishermen and small farmers must be safeguarded in such cases.
6.4 Technical Assistance
The Fishery Development Centre also needs to carry out the following: (i) render advice regarding the location of cages, the number of cages in each location, the species to be stocked, stocking rates, feeding, treatment of diseases, harvesting and marketing; (ii) the lakes have to be regularly monitored at least with regard to oxygen values and plankton quantities; the latter would be important for plankton-feeding fish and investigations have to be carried out as to whether the cages need to be moved seasonally to more plankton-rich areas.
6.5 Marketing
With regard to harvesting and marketing of cage cultured fish, the formation of associations seems possible although it would require considerable effort and time on the part of the Fishery Development Centre. The benefits to be gained by such association have to be demonstrated with the help of more willing groups.
6.6 Development of Artificial Feeds
As cage culture expands, the need for artificial feeds would arise and the Centre should try these in future. At present, one fisheries officer has been trained in feed technology; his talents must be utilized. Also two feed-pelleting machines have been imported and are due to be installed shortly in Hetauda and Bhairawa.
With regard to grass carp, the farmers should be encouraged to feed a variety of fodders for the present, since such a diet is likely to be more well-balanced than if only one type of fodder is used. Care must be taken not to introduce harmful feeds. Feeding with stale brewery wastes and one species of composite plant was followed by significant mortalities in three cages.
6.7 Further Experimentation with Stocking Rates
Experimentation is needed to determine the maximum stocking rates of the various species in the three lakes. This has already been discussed previously. In general, it is felt that stocking should be heavy enough to rear the fish economically to a commercial size of one-half to one kilogramme. It is felt that such rearing is more economical than raising only a few, very large fish.
6.8 Choice of Species
In general, in all lakes, plankton feeders should be reared to the maximum possible extent, since these fish will be the cheapest to raise. To the extent that production can be further improved by the addition of grass carp, this species should also be used. It is strongly felt that grass carp can be profitably raised in all locations in all three lakes. Common carp and rohu should, for the present, be considered incidental species, filling in unexploited niches in the cage ecosystem, and thereby increasing overall productivity of the cage.
6.9 Stocking Rates and Sizes
It is felt that common carp could have some value as scavengers and, at low densities, can contribute incidentally to overall production by feeding on the droppings of grass carp where the latter is cultivated as the principal species. The latter produces large quantities of poorly digested dung, if fed adequately. The excreta of other fish may, of course, also be consumed. In any case, given a Chinese carp as the major species, it is felt that common carp should be stocked at not more than one-twentieth the number of the major species, and that sizes of both species should be similar. The diet of the common carp should, if possible, be supplemented with dung, kitchen wastes, rice bran and other cheap feed.
The upper stocking limit for grass carp in a well cleaned cage with an unlimited fodder supply has yet to be determined. A realistic limit must take into account the total weight of live grass carp the owner can handle. This depends upon the circumstances of the owner most importantly, the availability of fodder and the composition of his family. In Sedi, the location with the most problems, considering the availability of grass, the maximum sustainable weight of grass carp per owner appears to be 150–200 kg. For owners in this location, therefore, it is felt that 500–750 grass carp per owner should be given as a first approximation. If experience shows them capable of handling more than this, the number can be adjusted upward.
Silver carp stocked at 9/m3 (.27 kg/m3) yielded commercial harvests after a year (Table 11). It is felt that stocking rates higher than this can be tried in future, particularly in Begnas and Rupa Lakes. In Phewa Lake, silver carp raised in Khapaudi (Table 3) showed encouraging results at low densities. Higher numbers per cubic metre should be tried in this location to ascertain commercial potential. Even in Sedi, where silver carp growth has been generally poor, encouraging results appeared in one cage, where the owner added large quantities of cow dung. This seems to have had a local fertilizing effect.
Rohu might best be stocked on a per square metre of cage surface basis. One fish per three to five square metres of cage surface appears suitable in the light of present experience.
For grass carp, a stocking size of 20 g appears economical. At sizes much smaller than this, the time taken to reach 20 g is excessive. The time investment is so great that the owner is advised to buy the larger, 20 g fish for the slightly increased costs. At sizes much larger than this, the opposite argument applies. The cost of rearing the fish to the larger size is less than the extra cost of buying the larger fish outright.
As in other species, of course, the mesh size of the cage will present an absolute lower limit to stocking size.
If fingerlings are in short supply, as was the case in 1978, available fingerlings must be spread among as many farmers as possible, so that each farmer receives a minimum economically useful number.
6.10 Timing of Harvesting
Harvesting of a cage, either partially or totally, could be carried out when: (i) fish have reached a marketable size; (ii) when, after reaching a reasonable size, further production would be negligible or negative, as for example during prolonged cold winter and when there are likely to be mortalities or; (iii) it is felt that daily production in a cage will be improved by replacing the old stock with a new stock of fingerlings. The latter situation may arise after periodically selling the faster growers and the slower growers are left behind.
6.11 Cage Maintenance
Just before restocking each year, the cage should be removed and inspected to see if any maintenance work is needed. Required work (painting, mending of holes, rewelding, rebinding of drums) can be done immediately and the cage reset for restocking.
6.12 Others
Once loans to the bank are paid off, fishermen must be encouraged to keep a certain amount of their proceeds from fish sales for maintenance and restocking of cages.
Government and private production of table fish should not compete. Prearranged timing of harvests and maximum daily limits by weight of Government fish sold to customers should help.
Interest is now being expressed in trying cage culture in other natural waters and man-made reservoirs of Nepal. Once the possible limitations of the site have been assessed, species and cage choice can be made accordingly. For instance, there are approximately 12 ha of water surface near the Kosi Barrage which appear suitable for cage fish culture. However, plankton feeders may not be suitable due to low plankton quantities present. An abundence of grass in the vicinity suggests that grass carp culture should be more appropriate. Other large bodies of water (e.g. Kulekhani reservoir) could be similarly investigated.
