Netherlands

by

Bert Steinmetz
National Correspondent
Directorate of Fisheries
P.O. Box 20401 2500 EK The Hague

I FISHERY BIOLOGY AND MANAGEMENT

1. Administration and policy

The last two years have been characterised by reorganizations in the Governmental services for the inland fisheries with the aim to cut down the expenditures and to improve the efficiency. At the end of 1987 the monitoring of fish stocks in inland waters by the Department of Fisheries has been stopped. These activities has been limited and thereafter concentrated in the Netherlands Institute for Fishery Research (RIVO).

The Chamber for Inland Fisheries, a legal body based on the Fishery Law, which has to control every agreement on the issue of fishing rights, will be restricted in its function. Therefore the concerning law has to be changed in 1988.

The Governmental extension focused on the management of fish stocks by the mainly private organizations of sport fishermen and by commercial fishermen has been stopped and will be privatized, probably in the Organization for the Improvement of Inland Fisheries (OVB); the organization financed on the basis of the issue of licenses.

The severe drop in the numbers of licenses issued to sport fishermen, which started some years ago, continued but a stabilization followed in 1987. The numbers issued in 1983/84, 1984/85, 1985/86, 1986, 1987 were 918.000, 741.000, 718.000, 614.000 and ca. 605.000.

Due to problems related with the heavy fyke fishery in lake IJssel (180.000 ha) the numbers of fykes used by the individual commercial fisherman has been stabilized at the level of 1985. The Governmental policy is focused on a certain decrease in this numbers because of the protection of the perch and pike-perch stock.

2. Research

Research by the RIVO in the lake IJssel revealed that like in foregoing years the 1986 yearclass of pike-perch was strongly reduced by eel fykemortality, whereas the 1987 yearclass was weak.

A marking and tagging study with sea trout in the river Rhine has been started as a part of the international attemp for the ecological rehabilitation of the Rhine. Also fish stock assessments have been intensified.

Eelstudies were continued. Immigration levels of glass eel in 1986 and 1987 were 48 and 57% respectively of the long time average. The application of tetracycline proved successful in establishing a correct method for ageing of eel. The burning and cracking method resulted in 90% correct readings. For eel management a statistical analysis of approximately 25 length frequency samples per year on a long time basis can reveal the state of the eel fishery. The eel stock of lake IJssel is almost depleted by the fishery.

Monitoring of eel on the infestation with Anguillicola crassa showed that most waters are infested. In heavily infested waters however eel show thickened or ruptured swimbladders without parasites. There was no difference in weight between infected and uninfected eel.

Utility studies of different types of fish passes have been continued, just as studies on differences in catches with mono- and multi-filament gill nets.

The Limnological Institute of the Royal Dutch Academy of Sciences studies the fish community structure in shallow eutrophic lakes. Special attention was payed to recruitment of larval cyprinids, the relation between feeding conditions and mouth width in eel and the feeding efficiency of zooplanktivorous bream.

The OVB did experiments in drainable ponds with pike-perch, carp, bream and ide to establich angling vulnerability and mortality after hooking. Also studies on the effects of stocking 0⁺ pike-perch of different sizes, of 0⁺ pike and 0⁺ catfish (Siluris glanis L.) on different cyprinids were studied in various pond series.

In field surveys the contribution of stocked 0⁺ pike-perch to the native pike-perch population was studied. Furthermore research to optimize fish handling was carried out.

At the University of Wageningen a research programme was started on Lake IJssel (200.000 ha) to figure out why year-class strenght of pikeperch and perch varies and how the management of the gillnet fishery on those species can cope with this variation. The management goal is not only a MSY but also a smaller variation in the annual yield. On behalf of possible management strategies an interactive simulation model was developed. This model is an age- and size- structured model written in CSMP. The research programme is executed in cooperation with the Netherlands Institute for Fisheries Investigations (RIVO, IJmuiden).

Young fish surveys were executed in July, August, September and November to follow the growth and feeding pattern, the spatial distribution and the decrease in numbers. Concurrently caught larger perch were used for growth studies. Backcalculations showed the influence of temperature on perch growth in Lake IJssel. Further, the LF-distributions of 2-group perch was strongly positively skewed, because this size of perch (11–18 cm) switches from feeding on zooplankton and macrofauna to feeding on fish (smelt).

The gillnet selectivity, was defined as a function of body girth instead of as a function of body length. Annual and seasonal variations in condition (food, reproduction) have a certain influence on body girth and so on gillnet selectivity.

Analysis of young fish surveys executed since 1970 in a restricted area and all over lake IJssel showed close resemblance. The survey over the whole of the lake reveals a fair indication of the total number of fish of year-class concerned, which will be caught in the gillnet fishery for pikeperch and perch some years later.

The research of the impact of un-exploited populations of pikeperch on the rest of the fish community was finished. Morphological limitations (gape width - maximum prey diameter) for pikeperch predation on other species were established. These were combined with growth rates in different water bodies to seen what age of predator is capable to prey on what age of prey.

An efficient survey sampling method for bream populations was developed. It encompasses the recording of the size at maturity, the LF-distribution and a restricted amount of age determinations. These data are used in the analysis of the LF-distributions in to distributions per year-class. In this way the indexing of year-class strenght of bream can be improved, when survey sampling for bream is executed once a year, but for a number of years in succession.

3. Management

Monitoring of fish populations for fisheries policy by the Directorate of Fisheries took place in 1986 and 1987, just as the extension to the responsible managers.

The OVB greatly enlarged the educational courses on subjects concerning fishery management. The courses cover now almost the whole field. It starts with an “Introduction course on fishery management” to which already more than 1000 managers of fish stocks participated, followed by two courses namely “The principles and problems of fish monitoring” and “The identification, biology and management of Dutch freshwater species”.

During the last two years the following courses could be added to the program (1) “Practical training electric fishery” and (2) “Practical fishery management”. Electric fishing is bound to several regulations of which one concerns an obliged practical training. During the one day course “Practical fishery management” participants have to develop a theoretical plan how to manage the fish stock in an inland water. In continuation of this course a new one will be developped in the near future, in which participants have to deal with a real field/case study.

Beside these courses an information programme about education of youth at angling clubs and at schools has been started. A complete education set will be presented in 1988. Moreover a course to support angling clubs in educating youth was started in the summer of 1987. Finally mention has to be made of the educational bulletin “OVB Bericht” and information leaflets.

II FISH CULTURE AND DISEASES

1. Administration and policy

Due the developments described under I.1 the extension to fish culturists was left to an increasing number of private organisations. An exception was made for the first and second line care for fish diseases, partly because of the certification needed for fish to be exported.

A regulation to prevent the import of major communicable fish diseases is in development and probably will be effective at the end of 1988. No import of freshwater fish and ornamental fish then will be permitted without the required certificate.

The infection of eel with the swimbladder parasite Anquillicola crassa spread quickley over the Netherlands. Special research capacity and funds have been earmarked for this problem.

2. Research

At the University of Wageningen (LUW) the studies on African catfish Clarias gariepinus were continued. New fish species e.g. common carp Cyprinus carpio, European eel Anguilla anguilla, Asian catfish Clarias batrachus and rainbow trout Salmo gairdneri were added to the research programme.

The results of the research of LUW on the artificial propagation of African catfish has focussed on the role of male stimuli (pheromones) on the proces of vitellogenesis. The research is financed by the Association for Applied Science and is carried out in cooperation with Royal University-Utrecht.

The gynogenetic common carp, obtained by irradiation of sperm and inhibition of the first mitotic division, is screened now on morphological, immunological and physiological parameters in order to determine the rate of inbreeding.

The cultivation of Asian triploid catfish is started by LUW to support the research programme of Universitas Brawijaya in Malang, Indonesia. The research is financed by Netherlands University Foundation For International Cooperation. Preliminairy experiments on the stimulation of sex differentiation by hormones in hatchery raised 18 months old eels are in progress. Effects of temperature and feeding level on the growth performance and survival rate of larvae of the African catfish were assessed. Growth performance was determined on the basis of growth rate, food conversion ratio, energy conversion efficiency, protein efficiency ratio and apparant net protein utilization. The nutritional value of several dry test diets for larvae were determined. Dried and decapsulated cysts of Artemia gave the best growth and survival rate.

An explanatory model predicting the effects of feeding level and feed composition on growth and growth composition of C. gariepinus fingerlings has been developed. The model explains growth, taking into consideration the processes of nutrient intake, digestion and absortion of nutrients. The model predicts reasonably well effects of feeding level and feed composition on growth and growth composition.

Research on methodology of bio-energetic studies on fish has continued. An experiment on adaption of glass eels A. anguilla to husbandry and feeding practices showed that natural feeds (cow spleen, cod roe) improved growth (SGR = 2 à 2,5% day-¹) and reduced growth variability and mortality.

Preliminairy research on husbandry of yellow eel showed that at low stocking densities (below ± 5 kg ^0.8m^-2) an increased aggression behavior resulted in a strongly increased mortality of up to 1% d^-1.

Research on summer mortality in rainbow trout has led to the belief that this is caused by metabolic stress induced by increased temperature and salinity. In cooperation with the Fish Disease Laboratory Weymouth (UK) an ELISA is developped for detection of specific antibodies against I.P.N. and B.N.D.

Research in cooperation with the Fish Disease Department of the University of California (Davis, California, USA) on catfish showed that neither the African nor the Aziatic catfish are sensitive to the Chanel Catfish Virus. C-terminal gastrin immuno reactive cells were found in the first part of the intestine of the African catfish. The number per 1000 cells was dependant on the feeding level.

In cooperation with the Institute for Systematics and Ecology of the Royal University in Leuven (Belgium) experimental infection of individual eel with infectious larvae of Anguillicola crassa was accomplished. After infection changes in plasma proteins, relative white bloodcell frequencies and fragility of erythrocytes were observed.

The OVB started feeding experiments with artifical feeds with 0⁺ pike-perch at the Experimental station in Beesd.

The aquaculture department of the RIVO focused its attention on research on the cultivation (feeding techniques etc) of glasseel to small yellow eel for fish culture purposes.

3. Management

Due to the cormorrant problem the OVB fish culture station near Lelystad a number of larger ponds totally 9 ponds of 96 ha. have been taken out of production. They are used for agricultural production.

III WATERQUALITY AND CRITERIA

1. Administration and policy

In the Rhine and the Meuse three hydro power-plants have been planned and partly already built. Fish migration up and down stream only partly could be safequarded. Especially the lacking of an overall study on guiding of fish was felt painfully. The IFM/EIFAC symposium on “Fishing with electricity” hopefully will give solutions.

2. Research

A large scale research program on the effects of planktivorous fish on waterquality was initiated by the Netherlands Institute for Inland Water Management and Waste Water Treatment. Several institutes cooperate in this program that was started in 1986 in drainable ponds of the OVB and in field situations. Pond studies focused on the applicability of European catfish for the regulation of 0⁺ cyprinids were initiated.

IV PRODUCTION STATISTICS

The production of fish in farms in 1986 and 1987 are given below.

* × 1000 numbers

The official landed catches of Lake IJssel were

* preliminiary data

Fishermen however are not obliged to sell their catches via official markets. About 30–50% is sold directly to traders.

V BIBLIOGRAPHIC REFERENCES

Boon, J.H., M. Ooms, Th. Wensing and E.A. Huisman 1987. Some aspects of Gass Bubble Disease in African catfish (Clarias gariepinus, Burchell 1822). Neth. J. of Agr. Sc., 35 (1): 63–66.

Boon, J.H., J.H. Smits, Th. Wensing and E. Lo. Plasma 1987 proteins in African catfish (Clarias gariepinus, Burchell 1822) and its relation with feeding level. Neth. J. of Agr. Sc., 35: 00–00.

Boon, J.H., R.W.A. Oorschot, A.M. Henken and J.H. van Doesum 1987. Ruptured Intenstine Syndrome of unknown etiology of young African catfish, Clarias gariepinus (Burchell, 1822) and its relation with the feeding level. Aquaculture, 63: 283–300.

Bovendeur, J., E.H. Eding and A.M. Henken 1987. Design and performance of a water recirculation system for high-density culture of African catfish, Clarias gariepinus (Burchell, 1822). Aquaculture, 63: 329–353.

Bovendeur, J. and E.H. Eding 1987. Design and performance of a water recirculation system to culture the African catfish. European Aquaculture Society. Aquaculture Europe '87, Amsterdam 1987. Bredene, Belgie, 1987; p. 13.

Cazemier, W.G. Fish and fisheries in the Dutch part of the river Rhine. Sciences de l'Eau (in print).

Dekker, W. 1986. Age reading of European eel using tetracycline labeled otoliths. ICES CM 1986/M:16.

Dekker, W. 1987. Preliminary assessment of the LJsselmeer eel fishery based on length frequency samples. ICES C.M. 1987/M:22.

Densen, W.L.T. van. Gillnet selectivity for pikeperch, Stizostedion lucioperca, and perch, Perca fluviatilis, caught mainly wedged. Aquaculture and Fisheries Management, 18: 1987; 95–106.

Donk, E. van, R.D. Gulati and M.P. Grimm 1987. Restoration by biomanipulation in a small hypertrophic Lake: preliminary results (submitted Hydrobiologia).

Doornbos, G. 1987. The fish fauna of Lake Grevelingen: the role of fish in the food chain of a man-made saline lake some ten years after embankment of a former estuary. Thesis Univ. of Amsterdam, 169 pp.

Heinsbroek, L.T.N. 1987 Effects of bodyweight, feeding level and temperature on energy metabolism and growth in fish. Energy Metabolism in Farm Animals, M.W.A. Verstegen and A.M. Henken (Eds.). Martinus Nijhof Publishers, Dordrecht, Boston, Lancaster, 478–500.

Henken, A.M., J.H. Boon, B.C. Cattel and H.W.J.Lobee 1987. Differences in growth rate and feed utilization between male and female African catfish, Clarias gariepinus (Burchell, 1822). Aquaculture, 63: 221–232.

Henken, A.M., A.M. Brunink and C.J.J. Richter 1987. Differences in growth rate and feed utilization between di- and triploid African catfish Clarias gariepinus (Burchel, 1822). Aquaculture, 63: 233–242.

Huisman, E.A. and C.J.J. Richter 1987. Reproduction, growth, health control and aquacultural potential of the African catfish, Clarias gariepinus (Burchell, 1822). Aquaculture, 63: 1–14.

Huisman, E.A. 1987 Aquaculture development: some thoughts. European Aquaculture Society. Aquaculture Europe '87, Amsterdam. Bredene, België, 1987.

Hurk, R. van den, W.J.A.R. Viveen, R. Pinkas and P.G.W.J. van Oordt 1987. The natural gonadal cycle in the African catfish, Clarias gariepinus: a basis for applied studies on its reproduction in fish farms. Isr. J. Zool., in press.

Klein Breteler, J.G.P. Intensive culture of pike perch fry with live food. In: Proceedings Aquaculture Europe '87 Amsterdam (in press).

Lammens, E.H.R.R., J. Geursen and P.J. Mac Gillavry 1987. Diet shifts, feeding efficiency and coexistence of bream (Abramis brama), roach (Rutilus rutilus) and white bream (Blicca bjoerkna) in hypertrophic lakes. Proc. V Europ. Conf. Ichthyol.: 153–162.

Lammens, E.H.R.R. 1986. Interactions between fishes and the structure of fish communities in Dutch shallow eutrophic waters. Thesis 100 p.

Lammens, E.H.R.R. Trophic interactions in the shallow eutrophic lake Tjeukemeer: bottom-up and top-down effects in relation to hydrology, bioturbation and predation during the period 1974–1985. Hydrogiologica in press.

Lammens, E.H.R.R. Biotic and abiotic interactions in Tjeukemeer: the effects of hydrology and planktivorous and benthivorous feeding on eutrophication. A re-evaluation of data. Hydrobiologia in press.

Machiels, M.A.M. and A.H. Henken 1987. A dynamic simulation model for growth of the African catfish, Clarias gariepinus (Burchell, 1822). II. Effect of feed composition on growth and energy metabolism. Aquaculture, 60: 33–54.

Machiels, M.A.M. and A. van Dam 1987. A dynamic simulation model for growth of the African catfish, Clarias gariepinus (Burchell, 1822). III. Effect of body composition on growth and feed intake. Aquaculture, 60: 55–71.

Machiels, M.A.M. 1987 A dynamic simulation model for growth of the African catfish, Clarias qariepinus (Burchell, 1822). IV. Effect of feed formulation on growth and feed utilization. Aquaculture: 64: 305–323.

Meyer, M.L., E.H.R.R. Lammens, A.J.P. Raat, M.P. Grimm and S.H. Hosper 1987. Impact of fish on zooplankton and algae in the fish ponds in the Netherlands (submitted Hydrobiologia).

Nie, H.W. de 1987. The decrease in aquatic vegetation in Europe and its consequences for fish populations. EIFAC Occasional Paper No. 19: 1–52.

Oordt, P.G.W.J. van, J. Peute, R. van den Hurk and W.J.A.R. Viveen 1987. Animal correlative changes in gonads and pituitary gonadotropes of feral African catfish, Clarias gariepinus. Aquaculture, 63: 1987; 27–41.

Peute, J., M.A. Zandbergen, H.J.Th. Goos, R. de Leeuw, R. Pinkas, W.J.A.R. Viveen and P.G.W.J. van Oordt 1987. Pituitary gonadotropin content and ultrastructure of the gonadotrops in the African catfish, Clarias gariepinus during the annual reproductive cycle in a natural habitat. Can. J. Zool., 64: 1718–1726.

Raat, A.J.P. 1987. Production, growth, condition and angling vulnerability of zander (Stizostedion lucioperca (L.)) in relation to the availability of prey fish in ponds (submitted Hydrobiologia).

Raat, A.J.P. 1978. Synopsis of biological data on the northern pike Esox lucius (Lineaus, 1758). FAO Fish Synop.

Raat, A.J.P. 1987. Effects of crowding and availability of food on growth and angling vulnerability in the two sexes of scaled and mirror patterned carp (Cyprinus carpio L.). Netherlands Journal Zoology (in press).

Resink, J.W., W.G.E.J. Schoonen, R. van den Hurk, W.J.A.R. Viveen and J.G.D. Lambert 1987. Seasonal changes in Steroid metabolism in the male reproductive organsystem of the African catfish, Clarias gariepinus. Aquaculture, 63: 59–76.

Resink, J.W., R. van den Hurk, P.K. Voorthuis, M. Terlou, R. de Leeuw and W.J.A.R. Viveen 1987. Quantitative Enzyme Histochemistry of Steroid and Glucuronide Synthesis in Testes and Seminal Vesicle, and its Correlation to Plasma Gonadotropin Level in Clarias gariepinus. Aquaculture, 63: 97–114.

Resink, J.W., R. van den Hurk, R.F.O. Groeninx van Zoelen and E.A. Huisman 1987. The Seminal Vesicle as source of sex attracting substances in the African catfish, Clarias gariepinus. Aquaculture, 63: 115–127

Richter, C.J.J., A.M. Henken, E.H. Eding, J.H. van Doesum and P. de Boer 1987. Induction of trylpoidy by cold - shocking eggs and performance of triploids of the African Catfish Clarius gariepinus (Burchell 1822) World Symp. on Selection, Hybridization, and Genetic Engineering in Aquaculture, Bordeaux, France, 1986. Selection, Hybridization and Genetic Engineering in Aquaculture of Fish and Shellfish for consumption and stocking. Prof. Dr. K. Tiews (Ed.), Berlin, Vol. II., 225–237.

Richter, C.J.J., A.J. Rothuis, E.H. Eding, F.G.F. Oyen, J.F.B. van Gellecum, C. Strijbos, F.J. Verbon and J.Th. Gielen 1987. Ovarian and body responses of the African catfish (Clarias gariepinus) to human Chorionic Gonadotropin (ChorulonR) and carp Pituitary Suspension, used in bioassay for estimating the gonadotropic activity of a crude carp powder preparation. Aquaculture, 62: 53–66.

Richter, C.J.J., E.H. Eding, H.J.Th. Goos, R. de Leeuw, A.P. Scott and P.G.W.J. van Oordt 1987. The effect of Pimozide-LHRAa and 17a-Hydroxyprogesterone on plasma steroid levels and ovulation in African catfish, Clarias gariepinus. Aquaculture, 63: 157–168.

Richter, C.J.J., W.J.A.R. Viveen, E.H. Eding, M. Sukkel, A.J. Rothuis, M.F.P.M. van Hoof, F.J.G. van den Berg and P.G.W.J. van Oordt 1987. The significance of photoperiodicity, watertemperature an inherent endogenous rythm for the production of viable eggs by the African catfish, Clarias gariepinus, kept in subtropical ponds in Israel and under Israeli and Dutch hatchery conditions. Aquaculture, 63: 169–185.

Schoonen, W.G.E.J., A.M. van Bennekum, J.G.D. Lambert, W.J.A.R. Viveen and P.G.W.J. van Oordt 1987. Steroidgenesis in Pre- and Postspawned ovaries of feral African catfish, Clarias gariepinus. Aquaculture, 63: 129–142.

Schoonen, W.G.E.J., J.G.D. Lambert, J.W. Resink, W.J.A.R. Viveen and P.G.W.J. van Oordt 1987. A quantitative study of steroid bioconversions in the testes of the African catfish, Clarias gariepinus (Burchell), under natural spawning and natural and cultivated non-spawning conditions. J. Endocrino., 112: 323–332.

Verreth, J.A.J. and K. Kleyn 1987. The effect of biomanipulation of the zooplankton on the growth, feeding and survival of pikeperch (Stizostedion lucioperca) in nursing ponds. J. Appl. Ichthyol., 3: 13–23.

Verreth, J.A.J. and H. den Bieman 1987. Quantitative feed requirements of African catfish (Clarias gariepinus, Burchell) larvae fed with decapsulated cysts of Artemia. I. The effect of temperature and feeding level. Aquaculture, 63: 251–267.

Verreth, J.A.J., V. Storch and H. Segner 1987. A comparative study on the nutritional quality of decapsulated Artemia cysts, micro-encapsulated egg diets and enriched dry feeds for Clarias gariepinus (Burchell) larvae. Aquaculture, 63: 269–282.

Verreth, J.A.J., M. Carillo, S. Zanuy and E.A. Huisman 1987. Investigación Acuicola en América Latino. Aquaculture research in Latin America. Lima, Peru, 1987. Wageningen pp. 451.

Verreth, J.A.J. and A. Gmelig Meyling 1987. The use of an industrial enzyme, Maxatase, to eliminate the adhesivenes of Clarias gariepinus (Burchell) eggs. European Aquaculture Society. Aquaculture Europe '87, Amsterdam, Bredene, België, 1987: p. 116.