(January 1986 – December 1987)
I. Fishery Biology and Management:
Major part of open waters in Czechoslovakia was used for sport fishing. As carp, forced fry of pike-perch, pike and other fishes are regularly released, it is possible to keep the catches growing (above 100 kg per ha commonly reached in coarse fishing waters and about 40 kg per ha in the trout waters), in spite of the increasing numbers of angler (above 300 000). Anglers' interest is mainly focused on carp, predators and salmonids. The small cyprinids highly prevail in open waters over other fishes: they constitute 80 % of both the abundance and weight of the fish stocks. Roach mostly pre-dominates, and also bream and white bream. The limited abundance of the most valuable fishes is due to the influence of the adverse factors of civilization, especially the waste waters generated by agriculture and industries, public sewage waters and other wastes; damage is also caused by acid rains, especially in northwestern Bohemia, in the vicinity of industrial centres. Small water courses are affected by the reclamation of land, bigger rivers are adversely influenced by the fluctuation of the water flow, navigation, manipulation with water level in the reservoirs of hydro-electric power stations and so on.
Increasing eutrophication brings about increasing production of algae, especially in the dam reservoirs. The chemical control methods have been given up and “special-purpose” fish stocks are being tested in stead, e. g. stocks of fish known to consume algae (silver carp). The so-called bio-manipulation practices are used in the fish communities in selected 42 dam reservoirs; the objective is to enrich and enhance the occurrence of predatory fishes and reduce the abundace of planktonophages. It is only in some places (especially in the dam reservoirs) that netting and electro-fishing are practiced to regulate the stocks by removing the overpopulated weed fishes. Stock material of the diminishing river fish species (nase, vimba bream, barbel, burbot) is produced in suitable sizes on an increasing scale on specialized fish farms. There is great interest in increasing the catches of eel which is imported as elvers from France. Stable traps installed in rivers and electro fishing gear serve for catching eel.
There are efforts to save the gene pool of some selected fishes. What deserves mentioning in this context is that a special huchen farm has been recently built for the production of one-year-old huchen to be planted in the Slovak rivers and other waters of sport fishing importance.
Fishery research in open waters is oriented to problems associated with:
II. Fish Culture and Diseases:
Fishery rese arch is included in the general state research assignment aimed at a reduction of the negative influences of environment through the use of biotechnological processes. This general research programme has three basic subprogrammes:
In the field of fish culture, the performance traits of the important gene pools of tench and carp were evaluated. The optimum breeds for hybridization were proposed for the major user of the research results (the State Fisheries Corporation), and the best pure lines and hybrids were given over to the State Fisheries for further improvement of breeding work. New breeding procedures for carp and tench (methods of gynogenesis) were worked out, with special orientation to the highest possible number of hatched fry. Methods of the use of synthetic hormones (LH-RH) and other peptides in controlled reproduction were tested for the controlled reproduction programme. Successful results of ovulation and sperm production were obtained in the supplemental fishes (tench, phytophageous fishes, grayling), and the preparations are now being introduced in practice. The immobilizing solution for the stripping of sheat fish was tested and positive results were obtained; patent for this solution has been applied for.
The technology of the production of fry in controlled environment with the use of warm waste water and in mixed stocks in ponds was further improved. The equation for the calculation of the specific growth rate of the reared fish was determined by computerized methods. A methodology was worked out for using computerized techniques in the planning and management of pond fish production. What can be considered promising are the results of rearing the fry of the imported fishes black buffalo and largemouth buffalo. As found on the basis of the evaluation of the mixed stocks of common carp and grass carp, grass carp is able already in the first year of its life to control very effectively the growth of the emergent aquatic plants (duckweeds), thus reducing the potential need for herbicides.
Problems of optimization of rearing stock fish and market fish in ponds were also solved, with respect to different production intensities. With stepwise increase of stock density in ponds with carp monoculture, the production levels were up to 3.3 tons per ha, with maximum fish yield of 5.3 tons per ha; in the polycultural stocks with grass carp, silver carp, and tench the maximum fish yield was 5.7 tons per ha. It is considered important that the individual losses of the studied fish species (lower than planned, except in grass carp) were independent of the degree of stock density and the level of intensification. The medium level of intensification with cereal diet was found to be most advantageous from the economic point of view; in the mixed stocks the fish production level obtained at the medium degree of intensification was 1.5 tons per ha, the relative food conversion coefficient being 1.88. Although the industrial system of fish culture markedly increased fish production, it significantly worsened the economic parameters. Production standards for the actual conditions of pond fish culture in Czechoslovakia were worked out on the basis of the obtained results.
Research on ponds exposed to pollution by organic waste waters showed that the stabilization ponds where the production levels are about 1 ton per ha, with low relative feed conversion coefficients, require special hydrochemical and hydro-biological care, especially in spring before the release of the stock fish and in the period when temperature increases above 10 °C, when daphnias are expected to develop. Major principles of management of these ponds were worked out.
Dried broiler litter was tested as an ingredient in the feed for market carp; the chick excrements were to replace the proteinaceous ingredients. Nine percent of dried broiler litter increased fish gains and reduced the costs of the feeds. The presence of the excrements in the diet had no influence on the smell and taste of carp flesh. Rapeseed food lecithin was also tested as a source of biogenic elements and energy in inclusion in the fish feeds.
Research on fish diseases was oriented to diagnostics, to the study of immunopathogenesis, methods of prevention and control of actual fish infections (Veterinary Research Institute Brno). A methodical manual on the diagnosis and prevention of the infectious necrosis of pancreas in salmonids was prepared for use on fish farms. As for the ichthyoparasitological problems, the research conducted by the Parasitological Institute of the Czechoslovak Academy of Sciences České Budčjovice was focused on the biology, distribution and ecology of the parasites and on parasites as the causative agents of serious parasitic diseases in fish stocks.
III. Fish and Polluted Waters:
The losses caused to Czechoslovak fisheries by the pollution of surface waters in the period from 1981 to 1985 were calculated. The average annual losses caused by calamity pollution of surface waters were about 10 million crowns, and the losses due to long-continued pollution of surface waters were estimated at 63 million crowns.
The regulations concerning hygienic requirements of the health-safety certification of new chemicals and preparations were ammended in 1986. Methods of evaluating acute toxicity to aquatic animals were worked out in detail within this ammendment, and Czechoslovak Standard čSN 46 6807 “Acute Toxicity Test in Fish” was revised. The methods of the acute toxicity tests were extended to cover also representatives of invertebrates; the system of evaluation of the results of the toxicity tests was elaborated in detail, three standard substances (ZnSO4.7H2O, K2Cr2O7, p-nitrophenol) were proposed for the verification of the performance of the tests, and so on. All the new developed chemicals and preparations now included in production are tested on the basis of this standard. The tests are performed by the Fisheries and Hydrobiology Research Institute at Vodňany and the Water Management Institute in Ostrava. Methods of toxicity testing in other representatives of water biocenose, including algae and aquatic bacteria, are being prepared at the institutes of the Czechoslovak Academy of Sciences located in České Budčjovice, Třeboň and other places.
Intensive efforts continued in the elaboration of the methodology of chronic toxicity tests in fish. The highest admissible concentrations of substances and preparations were determined from the point of view of fish culture requirements. The final draft method of chronic toxicity tests will be available in 1988.
The results of the acute and chronic toxicity tests are entered in the Czechoslovak data bank of substances contaminating aquatic environment, called LIDATOX (Limnologicae datae toxicologicae). Other toxicological methods were also worked out, e. g. toxicity tests in fish cell cultures, toxicity tests in young developmental stages of fish fry (called embryotests) and others. Attention was also paid to the methods of evaluation of toxic effects on fish. What appears promising is the use of the parameters of non-specific immunity in the evaluation of the sublethal action of toxic substances on fish.
IV. Production Statistics:
On the whole, Czechoslovakia has 52 200 hectares of fishponds. Of this area, the State Fisheries Corporation manages 40 600 hectares in the Czech Socialist Republic and 1120 hectares in the Slovak Socialist Republic. The remaining ponds belong to the Secondary Technical Fish Farming School, the Czech Anglers' Union and Slovak Anglers' Union, agricultural co-operatives, and other organizations. The Czech and Slovak Anglers' Unions use the ponds for the production of stock fish to be introduced in open waters where their members practice their sport fishing.
The amounts of market fish produced in 1986 in Czechoslovakia are shown in annexed Table 1.
The production data on the year 1987 are not yet available but they will hardly differ much from the 1986 data.
Tab. 1 Production of market fish in Czechoslovakia in 1986 (in tons):
|Fish species||State Fisheries Czech Socialist Republic||State Fisheries Slovak Soc. Rep. (data for 1985)||School Fish Farm, Fishery School||Czech Anglers' Union +||Slovak Anglers' Union+||Other producers/Estimate/||T o t a l|
|common carp||13 292||722||700||2304||1036||10||18 064|
|rainbow trout||593||98||-||105||237||-||1 033|
|maraena and peled||328||21||-||2||1||-||352|
|T o t a l||20 998|
+ angling in open waters