by
J. Dahl
National Correspondent
Danish Institute for Fisheries and Marine Research
Inland Fisheries Laboratory
Lisbrogade 52, DK 8600 Silkeborg
I FISHERY BIOLOGY AND MANAGEMENT
Salmonids
1.1 New liberation schemes for trout fry and fingerlings and revision of older ones have been set up for 10 individual river systems and 1 geographically well defined group of river systems.
1.2 Studies have been continued on the population dynammics of trout (sea-, brown-) in rivers, including migration, smolt production, spawning biology, homing and energy flow. The studies include an intensive tagging program, thus a total of 16,000 sea trout smolts and 1,154 sea trout spawners were tagged and released in the rivers involved.
1.3 Stocking experiments with salmon fry in a small tributary to the river Gudenå were continued. Furthermore a number of 1-year old and 2-year old salmon smolts of the Swedish Mørrumå-strain were tagged and released in the island of Bornholm, partly in one of the rivers, partly directly on the coast.
1.4 Experiments were carried out on the profitableness of stocking brown and rainbow trout directly in salt water, involving tagging through the biennium of 6,000 2-year old rainbow trout and 6,000 2-year old brown trout in two different coastal areas.
1.5 Studies were undertaken on the possible identification of different strains of trout by means of electrophoresis, in an attempt to select optimal spawners for the rearing of more suitable stocking material.
Eel.
2.1 Studies are continuing on the daily ascent of elvers and young eels into a number of Jutland rivers. The studies include observations of various hydrological and climatic parametres.
2.2 Analyses are undertaken on weekly samples of the glass eel ascent at the Vidå sluice (southwest coast of Jutland). The glass eels are analysed for their elementary chemical condition (content of water, lipid and protein) in relation to 1) the time of ascent within the course of the total ascent, 2) the pigmentation stage (“age”), and 3) the geographical distribution of the ascent. The study includes corresponding analyses of the glass eel ascent elsewhere in Europe.
2.3 Investigations have been continued on silver eel production in rivers and lakes and silver eel migration in spatiotemporal relations.
2.4 The long term experiments on the artificial maturation of silver eels by means of hormonal treatment are continuing.
2.5 Studies are continuing on ageing by means of otoliths of eels of known age originating from eel aquaculture.
2.6 Experiments have been carried out aiming at improving upon the construction of eel passes.
Other species.
3.1 Stocking of grass carp into small, closed water bodies is now undertaken by routine, after that previous year's experimental stockings have proved the suitability of this species for weed control in such waters. Facilities for the artificial propagation of grass carp have not yet been established, and so far stocking material is being imported from Austria under strict control by the veterinary and fishery authorities.
3.2 Studies are undertaken on the biology of dace with special reference to its coexistence with trout.
3.3 Studies are undertaken on the biology of burbot with special emphasis on its predatory habits in trout streams.
II FISH CULTURE AND DISEASES
Feeds and feeding in trout farming
1.1 Experiments are carried out on the applicability of various primary produce in fish feeds with special reference to reducing the phosphorous content, further to investigate the importance of the melting point of fish oils for fish growth and the utilization of the feed.
1.2 Experiments are carried out on the importance of high resp.low fat content of fish feeds when growing large rainbow trout under cooling water conditions.
1.3 Attempts to stimulate the osmoregulatory capacity of rainbow trout before transfer into salt water by adding thyroxine and salt to the feed.
Trout growth studies
2.1 The previously published growth model for rainbow trout has been tested for trout under normal production conditions in ponds.
2.2 Preliminary investigations have been carried out on the applicability of the model to the growth of tender fry, including growth in relation to egg size.
2.3 Investigations are carried out on the importance of the oxygen content of the water for food uptake, metabolism and growth of trout, including experiments on the possibility of including oxygen in the growth model.
Diseases
3.1 With regard to VHS new methods for detection of virus and circulating antibody to the virus have been developed and applied. The significance of free-living virus carriers in streams for the VHS eradication in trout farms has been studied.
3.2 ERM vaccines from commercial services have been potency tested under aquarium conditions as part of clinical trials aiming at official registration of the product. The distribution of the ERM infection in trout farms as well as free-living fish has been studied.
3.3 The transmission of PKD under field conditions was studied with special emphasis on the possible influence of water temperature and season on its efficiency. It has been attempted (so far unsuccessfully) to develop more sensitive methods for diagnosing the disease at early stages.
Veterinary services
4.1 The services undertake registration of VHS- and IPN-free trout pond farms. Admission to the IPN-register is conditioned only by preceding virological controls performed by the National Veterinary Laboratory (formerly State Veterinary Serumlaboratory).
4.2 By the end of 1985 a total of 520 trout farms were in operation. Out of these 455 were admitted in the VHS-register. During 1984–85 stamping-out programs were conducted and approved for 59 trout farms. During the same period recurrence of VHS occurred in 32 farms.
4.3 By the end og 1985 48 trout rearing farms were admitted in the IPN-register. A register for IPN-free production farms is being prepared and is expected to include about 50 farms for which a less intensive control than for the rearing farms is undertaken. During 1984–85 recurrence of IPN occurred in 3 farms.
III FISH AND POLLUTED WATER
Streams
1.1 Studies have been undertaken on the supply, transport and effect of nitrate, phosphorous and organic matter in streams.
1.2 Investigations are carried out on the denitrification and nitrification in streams in order to determine the magnitude of nitrate transformation in different types of streams.
1.3 Studies are undertaken on the possibility of identification of the nitrate components in livestock manure and silage juice.
1.4 Studies are carried out on the aeration and decomposition of organic matter and its importance for the oxygen conditions in streams. The work has concentrated on the primary producers - i.e. the benthic algae and the macrophytes.
1.5 Experiments are carried out on river restoration, including establishment of fish shelters, recreation of spawning beds, reduc tion of weed growth etc. The work is especially focusing on more proenvironmental techniques in river management.
Lakes
2.1 Experiments have been undertaken on biomanipulation of fish populations in order to improve water quality by reducing fish predation on the zoo plankton, thus increasing the grazing effect on the phytoplankton by the zooplankters.
2.2 Studies are carried out to pinpoint the dynamics of phosphorous in a shallow lake where the water quality is changing because of a reduced amount of phosphorous discharged.
Ecotoxicology
3.1 Experiments were carried on the effect on plankton in a eutrophic lake by different concentrations of tributyltin (a component of antifouling shipspaint). The work will form the basis for a more general description of the relations between the primary and secondary effect of an environmental toxin.
3.2 The previously reported investigations on the chemical, hydrological and biological effects on inland water organisms of the discharge of acid, ferruginous drainwater from agricultural areas mainly in those parts of the country where the soil is poor in natural buffers were terminated and has formed the basis for statutory regulations of agricultural draining activity in ochre potential areas.
IV PRODUCTION STATISTICS
Trout pond farming
1.1 The production (export + home market) of farmed trout (mainly rainbow trout) during 1983–85 amounted to
| 1983: | c. 23,800 m.t. | (= c. 428 Mio DKr.) |
| 1984: | c. 22,500 m.t. | (= c. 405 Mio DKr.) |
| 1985: | c. 21,300 m.t. | (= c. 383 Mio DKr.) |
1.2 The export of eyed ova of trout (rainbow trout, brown trout) during the same period amounted to
| 1983: | 32.0 m.t. | (= 10.6 Mio DKr.) |
| 1984: | 30.6 m.t. | (= 10.3 Mio DKr.) |
| 1985: | 25.0 m.t. | (= 9.0 Mio DKr.) |
The figures for 1985 only represent the period January-November incl.
Inland waters
According to the official Danish fishery statistics the total catch in Danish inland waters in 1983 and 1984 amounted to 412 and 452 m.t. respectively. The percentage species distribution of the catch was as follows for the biennium: eel 28%, bream 12%, trout (sea-, brown-) 8%, roach 8%, pikeperch 7%, pike 5%, perch 4%, rainbow trout 3% and other species 23%. The statistics for 1985 were not available at the time of reporting.
BIBLIOGRAPHIC REFERENCES
Subcommission I
Ansbæk, J.: The fishes of the river Vidå. (in Danish). - Sportsfiskeren 59(2) : 10–11, 1984.
Brookes, A.: Recommendations bearing on the sinuosity of Danish stream channels. - Miljøstyr. ferskv.lab., Publ. no 20, 130 pp, 1984.
Iversen, T.M.: The watering of fields and its influence on the ecological condition of streams. (in Danish). Vand & Miljø 1(3): 29–33, 1984.
Jeppesen, E. & Thyssen, N.: Models for the biological structure of streams. (in Danish). -Vand & Miljø 2(1): 13–18, 1985.
Kern-Hansen, U.: Streams. Ecology and planning. (in Danish). - Miljøstyr. Ferskvandslab., Publ. no 21, 107 pp, 1984.
Larsen, K.: The sea trout spawning run into Danish streams 1900–1960. I. The islands east of Storebælt. (in Danish with English summary). - Medd. Ferskv. fiskerilab. no 1, 65 pp, 1984.
Larsen, L.K.: The lake trout in lake Hald sø. (in Danish). - Sportsfiskeren 60(5): 20–21, 24, 1985.
Markmann, P.N.: Obstructions and fauna passage in streams. (in Danish). - Vand & Miljø 1(2):21–25, 1985.
Markmann, P.N. & Rasmussen, G.: The fishery value of our inland waters. (in Danish). - Vand & Miljø 2(3): 105–109, 1985.
Mortensen, E.: Production of benthic invertebrates and energy dynamics of brown trout, Salmo trutta L., in the springbrook community of Bisballe bæk, Denmark. - Nord. Limnol. Symp. 3–4 April 1984:177–187.
Mortensen, E.: Energy flow in trout (Salmo trutta L.) and benthic invertebrates of the springbrook community of Bisballe bæk, Denmark. - J. Ictiol. Iberica I, 1984.
Mortensen, E.: Oxygen consumption and energy requirements of brown trout, Salmo trutta L., in Bisballe bæk, Denmark. Preliminary results. - J. Ictiol. Iberica II, 1985.
Thyssen, N.: The effect of reduced discharge on the ecology of streams. (in Danish w. English summary). - Vatten 41(3):172–178, 1985.
Subcommission II
Alsted, N. & Hansen, P.: The taste of trout. II Freshwater and saltwater culture. (in Danish). - Ferskv.fisk.bl. 82(10):258–260, 1984.
Bregnballe, F.: The taste of trout. (in Danish). - Ferskv.fisk.bl. 82(8):206–208, 1984.
Bregnballe, F.: Danish mariculture of rainbow trout - the historical development. (in Danish). - Niche, Nord. Tidsskr. Krit. Biol. 3/1984.
Bregnballe, F. & Jokumsen, A.: Culture of large rainbow trout in seawater -esp. cooling water. (in Danish). - Medd. Forsøgsdambruget no 75, 139 pp., 1985.
Dahl-Madsen, K.I.: Developmental possibilities for aquaculture in Denmark. (in Danish). -Vand & Miljø 2(3):111–112, 1985.
Dalsgaard, I, From, J., Hørlyck, V. & Kehlet, N.P.: Outbreak of enteric Red Mouth Disease in Denmark. (in Danish). - Ferskv.fisk.bl. 82(9):231–233, 1984.
Forchhammer, K. & Heerfordt, L.: Aeration systems for aquaculture purposes. (in Danish). - Nord. Aquacult. 1(4):13–15, 1985.
From, J. & Hørlyck, V.: PKD - a new disease in Danish pond farms. (in Danish). - Ferskv.fisk.bl. 82(4):90–93, 1984
Hansen, P.: The taste of trout. III. Seasonal and sexual differences. (in Danish). - Fersk.fisk.bl. 82(11):289–291, 1984.
Hørlyck, V. & Kehlet, N.P.: Clinical testing of vaccines against redmouth disease. (in Danish). - Ferskv.fisk.bl. 83(11):286–289, 1985.
Jokumsen, A., Solberg, S. & Hørlyck, V.: Thermotherapy and sterility in trout. II. (in Danish). - Medd. Forsøgsdambruget no 69, 1985.
Krog, C.: Aquaculture and the promotion of fish populations. (in Danish). - Nord. Aquacult. 1(2): 21–22, 1985.
Minck, F., Mellergaard, S. & Bjerregaard, J.: The gill parasite, Dactylogyrus, of eels. (in Danish). - Fersk.fisk.bl. 82(11):293–294, 1984.
Olesen, N.J. & Vestergård Jørgensen, P.E.: Development of more sensitive laboratory methods for identification of virus and virus-antibodies in trout exposed to infection with Egtved-virus, cause of the VHS disease in trout farms. (in Danish). - ed. by Fællesudv. for det danske ørrederhverv. 1984.
Olesen, N.J. & Vestergård Jørgensen, P.E.: Total immunoglobulin in rainbow trout. Estimation of IgM concentration in sera from rainbow trout from different environments. -Stat. vet. Serumlab., Århus, Oct. 1985.
Olesen, N.J. : Fish diseases on database. (in Danish). - Stat. vet. Serumlab., Århus, 1984.
Olesen, N.J. : PKD in 1984. (in Danish). - Ferskv.fisk.bl. 83(5):126–129, 1985.
Rasmussen, K.: Whitefish (Coregonus) in aquacultural perspective in Denmark. (in Danish). -Nord. Aquacult. 1(2): 33–35, 1985.
Solberg, S. Jokumsen, A. & Hørlyck, V.: Thermotherapy and sterility in trout, (in Danish). - Medd. Forsøgsdambruget no 68, 1984.
Vestergård Jørgensen, P.E.: Egtved disease. (in Danish). - in: “Akvakultur og nye danske erhvervsmuligheder”,: 51–57. - ed. by Akad. tekn. Vidensk., 1984.
Vestergård Jørgensen, P.E.: Virus data form for Egtved virus. - WHO Collab. Centr. for Coll. and Eval. of Data on Compar. Virology, pp 1–23, 1985.
Subcommission III
Andersen, J.M. & Christensen, J.H.: The content of heavy metals in sediments from lakes and coastal marine areas. (in Danish). - Vand & Miljø 1(1): 20–25, 1984.
Brix, H. et al.: Sewage purification in reed marsh purification plants. (in Danish). - Stads- & Havneing. 75(4): 110–113, 1984.
Christensen, L.B.: Ochre purification. -Methods, purifying effect, management and economy. (in Danish). - Vand & Miljø 1(3):11–15, 1984.
Henriksen, H.J., Hansen, B. & Jørgensen, F.: Choice of methods in calculation of the transport of substances in streams. (in Danish). - Stads- & Havneing. 76(1):16–21, 1985.
Johansen, N.B. & Harremoes, P.: Pollution by rainwater discharge into the river Mølleå. (in Danish). - Stads- & Havneing. 75(9):220–226, 1984.
Kirkegaard, J.: The extent of agricultural discharge and its influence on the condition of streams and lakes. (in Danish). - Vand & Miljø 1(3):22–28, 1984.
Kvist, K.K.: The load of illegal discharges from farms. (in Danish). - Stads- & Havneing. 75(2): 46–48, 1984.
Orbæk, K.: Pesticide residues in Danish food. (in Danish w. English summary). - Publ. no 107, Stat. Levnedsmidd. inst., 140 pp. 1985.
Riisgård, H.U.: Outline of the ecotoxicology of mercury in the aquatic environment. (in Danish). - Vand & Miljø 2(4): 163–167, 1985.
Roulund, J. & Andreasen, K.: An experimental project on comparative methods for the removal of nutrients. (in Danish). - Stads- & Havneing. 76(6–7) :139–142, 1985.
Skaarup, J. & Neergaard-Jacobsen, B.: Purifying mechanisms in reed marsh purification plants. (in Danish). - Vand & Miljø 1(1):26–30, 1984.
