by
K. Tiews 1
National Correspondent
I FISHERY BIOLOGY AND MANAGEMENT
Monitoring of coregonids in the Starnberg Lake were continued by the Bayerische Landesanstalt für Fischerei. Apart from experimental fishing and the analysis of catch statistics, larval catches and echo-surveys were carried out with the special aim to improve the prediction of catches. Survey work was extended to the Lake Constance and to some oligotrophic lakes in the National Park of Berchtesgaden. Tagging experiments were carried out to check the success of coregonid stockings in lakes. It was estimated that 14 % of the eels stocked in lakes of the Alpes during 1976 – 1983 were recaptured.
The Institut für Seenforschung und Fischereiwesen, Langenargen, assessed the benefits of large-scale stockings of coregonids in the Lake Constance and came to the conclusion that the balance has to be considered as positive. Using the coregonids as an example, the long-term influence of eutrophication in the Lake Constance on the fish stocks was studied. From formerly 4 races of coregonids, only the plankton feeders do continue to play practically a role. A mixing of the races has occurred. All races able to feed plankton go over to plankton-feeding during summer, whereby a niche-hyrarchy can be observed. This fish grows faster, condition factor and fat content increases. The fish races distribute themselves new, and the former fish societies mix themselves. Egg number, egg size, spawning time, length of maturation, age of maturation, and hatching rate are being influenced. Hybridizations are favourably influenced. Parasite infestation increases. If the nutrient input into the lake exceeds a certain point, it is expected that this trend might revert.
Various assessments of lakes and rivers in Baden-Württemberg were carried out on a routine basis.
The Department for General Limnology of the Max Planck-Institut für Limnologie, Plön, continued its ecosystem study in the Lake Pluβ. Research concentrated on the coupling of the metabolism of algae and bacteria and on enzymatic adaptations on the living conditions in the lake. The bacteria studied are in the position to maintain a constant metabolic rate despite of fluctuating water temperatures by means of activating enzymes with differring temperature optima. Taxonomic and population dynamical studies of the phytoplankton as motor of the lake metabolism play an important role in the ecosystem analysis. Phytoplankton - zooplankton relationships as well as aspects of vertical migrations of zooplankton are an integrated part of plankton ecological studies.
II FISH CULTURE AND DISEASES
The Institut für Küsten- und Binnenfischerei of the Bundesforschungsanstalt für Fischerei continued its effort to introduce eel farming in the Federal Republic of Germany. The production of consumption eel in the experimental station of Emden could be increased to 18 kg per m2. The cost efficiency of eel farming could be furtherly improved by means of an improved technology and better measures for disease prevention. Trials to test the thermal effluents of the nuclear power plant Unterweser in Esensham were carried out and completed. It could be shown that the thermal effluents of this power station are suitable for eel farming. The development of a silo technology to rear elvers up to the size suitable for stocking eel farms, were completed. The eel farming experiments faced for the first time the problem of an infestation of the elvers with the gill parasite Dactylogyrus. The use of farmalin, masoten and chloramin bathes were unsatisfactory.
Feeding experiments with carps, eels and sheatfish were continued at the Institut für Küsten- und Binnenfischerei. In cooperation with the University of Tel Aviv a method could be developed to produce a carp gonadotropine with a standardized known activity.
In the frame of the German-Israelean cooperation in the field of aquaculture, hybridization experiments with pure carp lines from Israel, Germany and Czechoslovakia could be completed at the Bayerische Landesanstalt für Fischerei, Starnberg, It was not possible to demonstrate a clear advantage in any of the lines, which would hold true throug all growth periods. Hybrids showed slightly better growth. The results of the best pure lines and the worst hybrids overlapped however. Interactions between genotypes and test areas (Israel resp. Germany) could not be recognized.
Methods for the controlled reproduction of the tench were tested at the same institute. Hypophysation of small females was especially successful. The spawning of eggs on artificial spawning substrate was unsatisfactory.
Cryopreservation of sperm with various species was continued. Fertilization experiments using cryopreserved sperm and fresh sperm was in several cases equally successful.
Rearing experiments with coregonid fry kept in illuminated underwater net cages was successful.
The Institut für Siedlungswasserbau of the University Stuttgart in cooperation with the University Hohenheim tested if Perca fluviatilis can be cultured. Water quality criteria for the husbandry of the fish were studied as well as reproduction techniques and the feeding of the species.
The Institut für Hydrobiologie und Fischereiwissenschaft of the University of Hamburg studied the autecology of Colossoma macropomum in the Amazone. The fish is considered a potential candidate for inexpensive aquaculture in the Amazone area.
The Staatliche Fischseuchenbekämpfungs- und Fischgesundheitsdienst Niedersachsen started in cooperation with the Staatliches Veterinäruntersuchungsamt Hannover a program for the statistical treatment of some 6000 records related to fish health conditions in fish farms located in Niedersachsen. The state of Lower Saxony (Niedersachsen) has available now 4 officially certified disease-free aquaculture installations according to the new fish disease protection law issued by the state government. They are certified as free of IPN, VHS, SVC. Three further installations are in the process to reach this status. In 1983 the following records of outbreaks of fish diseases were made in the state of Lower Saxony: 8 IPN, 20 VHS, 37 furunculosis, 10 erythrodermatitis, 8 vibrio and 3 ERM (Enteric Redmouth Disease) and 10 PKD. In comparison to the preceeding years, IPN was found to be slightly declining. ERM, which is a new disease, is spreading in Northern Germany.
Three cases of edwardsiellosis in eels and sheatfish (of foreign origin) were reported under warmwater aquaculture conditions.
The Tiergesundheitsdienst Rayern e.V. in Grub studied the conditions under which fish in angling waters become infested with diseases. Studies on the occurrence of virus infections in freshwater fish were continued in Bavaria. During the years 1977 to 1981, 1413 samples of fish and fish eggs of 490 pond farms in Bavaria were checked on virological diseases. In 236 cases the VHS virus was detected, in 87 IPN, in 44 SVC, and in 1 sample of pike fry a Rhabdovirus.
Serological studies on 1085 blood samples of salmonids and 1963 blood samples of cyprinids demonstrated the wide distribution of VHS, IPN and SVC virus in pond fisheries. In 28 of 47 farms fish with neutralized VHS antibodies were found, in 30 of 47 farms fish with IPN antibodies, and in 51 of 59 farms fish with SVC antibodies.
At the Institut für Zoologie und Hydrobiologie of the University of Munich studies on the following subjects were continued: Spreading of fish virus by means of living and dead vectors; stability and abundance of the IPN virus in the sperm of rainbow trouts; quantitative identification of SVC antigens with the help of immunofluorescence and immunoper-oxydaseplaque techniques.
At the Institut für Hydrobiologie und Fischereiwissenschaft of the University of Hamburg gill damages of trouts in intensive aquaculture installations were studied, as well as the influence of water quality on the parasitization of carp during overwintering.
At the Institut für Seenforschung und Fischereiwesen, Langenargen, studies concentrated on the importance of the total gas pressure for the outbreak of the “Gasblasen-disease”. A method to determine nitrogen gas in situ was developed.
III FISH AND POLLUTED WATER
The Institut für Küsten- und Binnenfischerei of the Bundesforschungsanstalt für Fischerei completed its studies how to reduce the pollutant content of eels caught in the river Elbe by means of aquaculture. The study revealed that consumption eels of autumn catches are unsuitable for intensive aquaculture because of their high share of silver eels. This method is, however, also for the non-silver eels unprofitable because of too high mortalities, too low growth potential of the consumption sized eel, and because of unfavourable food conversion. In most fish the decline of pollutant concentration is practically neglectible so that most of the eels were still not consumable although having been kept for half a year under farming conditions.
The contents of mercury, HCB and HCH were studied.
Studies on 2 years' old sheatfish and 5 years' old channel catfish which were grown at the Institut für Küsten- und Binnenfischerei entirely with commercial pellet feeds, showed that the content of mercury, HCH, PCB, Dieldrin, Lindan as well as total DDT was much below the permissable rates according to the German food law.
Rainbow trouts fed with 1 ppm Cadmium-contaminated trout feeds showed large changes in their behaviour in electrophysiological experiments, in their blood picture, their organs and their skeleton.
In cooperation with the Technical University of Hamburg a filter for the elimination of suspended matters in aquaculture circulation systems was developed at the Institut für Küsten- und Binnenfischerei. In fish water suspended matter are difficult to settle and therefore consume oxygen, disturb nitrification and cause higher numbers of bacteria.
The Bayerische Landesanstalt für Wasserwirtschaft, München, studied the extent and major causes of fish kills in 7 districts of Bavaria. The occurrence of fish kills shows increasing tendency. Fish kills in standing waters including in pond fisheries are much more frequent than in flowing waters. Main causes are oxygen deficiencies due to the disposal of silage waters and manure (22.2 %), followed by lack of oxygen due to wrong farming practices (9.6 %), inflow of poisoneous industrial waste water (9.1 %), as well as waste waters of communities (8.8 %). Some 28 % of all fish kills with a total loss of 7.3 tons could not be clarified at all.
The Bayerische Landesanstalt für Wasserforschung has completed a report on the PCB and pesticide status of Bavarian waters during the years 1977 to 1982. Work on the methodology for PCB analysis has been continued.
At the Institut für Hydrobiologie und Fischereiwissenschaft of the University of Hamburg the development of fish tests for the study of ecotoxicological effects of pollutants in waters was continued.
IV PRODUCTION STATISTICS
Inland fishery statistics are officially collected only every ten years. The last survey was completed in 1981. Production figures for the years in between are rough estimates by the German Fisheries Association. According to these, the following fish production was made in 1983:
| Consumption rainbow trouts | 13500 tons = 88 million DM |
| Consumption carps | 6800 tons = 27 million DM |
| Consumption fish from river and lake fisheries | 4000 tons = 17 million DM |
| Total | 24300 tons = 132 million DM |
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