P. Ahlfors, P. Kummu and K. Westman
Finnish Game and Fisheries Research Institute
Helsinki, Finland
ABSTRACT
The earliest attempts to introduce carp to Finland were made in 1861, but results were not obtained until farming and stocking were begun again in the fifties. Juveniles are raised in earthen ponds, primarily on natural feed. A total of about 170 000 juvenile carp of one year and older were stocked from 1956 to 1981 in inland and brackish waters between 60° and 68°N, and 13 000 juveniles of two years and older were marked with Carlin tags. Catch varied between 0 and 336 kg/1 000 stocked individuals. Stocking was not economically profitable. As these estimates were made from returned tags, they appear low because of tag loss or failure to report a proportion of tags recaptured. Furthermore, Finnish fishermen are unaccustomed to fishing for carp.
The best results were obtained with two or three year old juveniles, at least 18–20 cm long and weighing 150 g or more. In eutrophicated waters with a great deal of vegetation, carp had an incremental weight gain during the year of stocking of up to 1 000–1 500 g. The largest tagged carp caught weighed 5 100 g and the largest untagged 11 900 g.
Under Finnish conditions, carp do not appear to be able to form self-reproductive populations, since the juveniles die during the first winter in natural waters. Carp has not been observed to have any harmful effects on the water systems. Interest in carp stocking is increasing, especially in eutrophicated waters in southern Finland.
RESUME
Les premiers essais d'introduction de la carpe en Finlande remontent à 1 861. Toutefois, il a fallu attendre, pour obtenir des résultats, que l'élevage et le repeuplement reprennent au cours des années cinquante. Des juvéniles sont élevés dans des étangs de terre avec, le plus souvent, une alimentation naturelle. De 1957 à 1980, on a utilisé environ 170 000 individus d'un an ou plus pour repeupler les eaux intérieures et les eaux saumâtres entre 60° et 68°30'N. Des juvéniles de deux ans et plus servant au repeuplement ont été marqués (marques Carlin, 13 000 individus au total, 46 groupes de marquage dans 33 sites de repeuplement). Les captures ont varié entre 0 et 340 kg pour 1 000 individus mis à l'eau. Le repeuplement n'a eu aucun avantage économique. Toutefois, le taux de survie des carpes mises à l'eau n'a pas été aussi faible qu'on pourrait le penser compte tenu du nombre de marques récupérées (certains se sont perdues, d'autres n'ont pas été renvoyées). De plus, les pêcheurs finlandais n'ont pas l'habitude de pêcher la carpe.
Les meilleurs résultats ont été obtenus avec des juvéniles de deux ou trois ans d'au moins 18–20 cm et 100–150 g et, lorsque les populations de brochets étaient importantes, avec des juvéniles de 25 cm et 250 g. Dans les eaux eutrophes à forte végétation, le poids des carpes pouvait augmenter de 1 000–1 500 g durant l'année de repeuplement. La plus grosse carpe marquée que l'on a capturée pesait 5 100 g; la plus grosse carpe non marquée 11 900 g.
Compte tenu des conditions qui règnent en Finlande, la carpe ne semble pas à même de former une population reproductrice; les juvéniles meurent durant leur premier hiver dans les eaux naturelles. Pour autant que l'on sache, la carpe n'a eu aucun effet nuisible dans les réseaux hydrographiques. L'intérêt s'accroît pour le repeuplement en carpes, notamment dans les eaux eutrophes du sud de la Finlande.
Carp (Cyprinus carpio) has been cultivated in its native Asia for thousands of years. Because of its cultivation by Man, carp very early on spread beyond its original range of distribution. It was brought to Europe quite possibly as early as the time of ancient Rome, but at the very latest by the 13th or 14th century. In many areas carp is frequently either deliberately stocked or individuals have escaped from a fish farm and formed a natural population. Today carp is found in all parts of the world with the exception of Antarctica (cf. Huet, 1971).
Carp was brought to Finland fairly late, in 1861. The earliest attempts at carp cultivation were made in the latter half of the 19th century in southern Finland (Malmgren, 1883; Sandman, 1892; Wuorentaus, 1938). These stocks did not become established because of a lack of proper facilities for overwintering. In addition, at that time sharp variations occurred in the climatic conditions, for example, a sudden return to harsh winter conditions after the spring thaw.
The next attempt in the thirties in central Finland also failed. In this case, the suspected reason was a summer too cold to allow spawning (Saari, 1937, 1939; Wuorentaus, 1938).
In 1951, 40 one and two-summer old carp were introduced into Finland from the Aneboda Fish Culture Station in Sweden to the Porla Fish Culture Station in southern Finland (60°15'N). Initially the aim was simply to see if carp could be cultivated so far north. The following spring 18 carp were left, which thrived in the Station, and a further 300 one-year old individuals were imported in 1955 to increase the stock. At this point the original aim was extended to see if carp could succeed in natural waters and to study its possibilities in the management of eutrophicated waters. In 1955, the brood fish in Porla also reproduced for the first time thus making continuos cultivation possible (Kajosaari, 1980; Sormunen and Kajosaari, 1975).
Carp were imported into Finland for a third time during the fifties. In 1958 450 one-summer old, third-generation offspring of a cross between Galician mirror carp and Amurian “sazan” carp were imported from the Ropsha Experimental Station near Leningrad (Kajosaari, 1959). The aim was to find a race of carp which would be able to withstand the winter better than ordinary carp. It was thought that such carp would be easier to cultivate and would be suitable for stocking in waters in northern Finland, as well as possibly forming a self-reproductive population in natural waters.
The first crossbred carp were hatched in Porla in 1963. The last brood fish in this population were taken out of the experiment in 1977. No significant advantage of the crossbred carp over the ordinary carp could be demonstrated (Sormunen and Kajosaari, 1975). This may also have been affected by the narrow genetic base of the crossbred carp fingerlings imported to Finland. Under hatchery conditions, the crossbred fingerlings overwintered slightly better than did the ordinary carp fingerlings. As mature adults, the crossbred carp exhibited a slow rate of growth.
In the following we will deal primarily with the experiences obtained with the offspring of carp imported from Aneboda, Sweden, to Finland.
Carp fingerlings cannot survive winter conditions in Finnish natural waters during their first year. For this reason, juveniles are raised in a hatchery until they are two-summers or two-years old before stocking. With the exception of the last two or three years, the carp raised in Finland have been cultivated in the Porla Fish Culture Station in Lohja. Cultivation has been run in one phase using the “uncontrolled natural reproduction in ponds” method described by Huet (1971). This cultivation has been described by Sormunen and Kajosaari (1975) and Kajosaari (1980).
For spawning brood carp are moved from the winter ponds to spawning ponds with earth bottoms and considerable vegetation at the beginning of May. The maximum depth of these ponds is 1.5 m and their surface area is generally 0.5–0.75 ha. The number of brood fish is between 30 and 34 individuals/ha; and the sex ratio is 2:1 females:males. The carp spawn freely in the ponds. The time of spawning is regulated mainly by the weather. In warm springs spawning may be as early as May but in cool springs as late as the end of June. An even, rapid, warming spell is most certain to bigger spawning and no spawning was observed at temperatures below 20°C.
In Porla, conditions are such that the brood fish cannot be moved out of the spawning ponds during the summer, so that these ponds are also raising ponds for juveniles during their first summer. The brood fish and juveniles feed on natural food in the ponds. As a supplementary feed, the juveniles are given cracked wheat at the end of summer. In the autumn, the ponds are emptied, the brood fish moved to winter ponds and the fingerlings taken indoors. Because of the natural method used and the variations in the weather during Finnish summers, the results of cultivation vary considerably from year to year, both as to number of fingerlings and their size. In the best case, the density of one-summer old fingerlings obtained was 2 individuals/m2 (Kajosaari, 1966). The average size of juveniles varied from below 10 g to nearly 50 g.
The first winter is critical to the adaptation of carp fingerlings to Finnish climatic conditions. The loss of juveniles during this period has been attributed to the insufficient amount of stored nutrients in one-summer old fingerlings. This means that they do not have enough energy to maintain basal metabolism during the period when the water is too cold for them to feed (Kirpitschnikov, 1957).
During the first winter in the Porla Fish Culture Station, spring water at an even temperature of +6.3°C is used for rearing. The fingerlings are divided into two size classes and placed in 1–1.5 m2 wintering basins made of wood, fibreglass or aluminium. Spring water is circulated at the rate of 1 1/minute/2–3 kg of fish. The depth of the water in the basin is about 15 cm, and the density of fingerlings generally 15–30 kg/m2.
As the winter progresses, the juveniles are fed with dry salmon feed once or twice a week. According to Huet (1971), carp stop eating when the temperature falls below +5°C. In Porla, however, carp in an experiment stopped eating only when the temperature fell to +2.5°C (Kajosaari, 1962). It is possible that the carp population in Porla is slowly becoming adapted and acclimatized to local conditions.
In the Porla Station the carp fingerlings are given an NaCl bath (1.5 percent, 15 minutes, no aeration) as needed during the winter to prevent gill and skin parasites.
With these methods, the losses during the first winter at Porla were only about 10 percent and were highest with the smaller fingerlings.
For the second summer, the fingerlings are moved to earthern ponds with lush vegetation when the water in the ponds has reached the same temperature as that in the wintering basins (+ 6°C). The surface area of the ponds is 0.1–0.75 ha and their average depth about 1 m. The juveniles feed on natural food and are given small amounts of cracked wheat as a supplement. Boiled potatoes, ground fresh fish and dry salmon feed have also been found to be good supplemental feed.
A good carp pond in southern Finland produces at least 100–300 kg of carp/ha. If a weight of 150 g is desired for two-summer old carp, then between 1 000 and 2 000 one-year old fingerlings per hectare should be stocked into the growing ponds at the beginning of the second summer (Ilmarinen, 1982). During the second winter, the carp of two summers are placed in the same wintering ponds as the mature brood fish. The depth in the pond used is fairly even, 1–1.5 m, with a maximum depth of 2 m and a surface area of about 0.1 ha. There is a slight current of water, which cuts across only a narrow section of the water mass in the pond.
The advantage of the simple cultivation method used in Porla is that the fish require very little handling, transfer or care. The greatest drawback is the short, first growing season for fingerlings. The Finnish Game and Fisheries Research Institute intends to begin research and development of controlled reproduction methods suitable for Finnish conditions, intensive rearing of carp fingerlings during their first summer with dry feed developed especially for carp, and the rearing of carp in the warmwater effluents of power plants.
The carp imported from Aneboda first spawned when they were five years old and the largest individual weighed 4.5 kg. To maintain genetic variability, the stock of brood fish is kept larger than production requires and supplemented from time to time by leaving a few young individuals to grow with the brood fish in the spawning ponds. The last imported carp in 1951 died during the winter of 1980–81 and was thought to have still spawned in the spring of 1980.
A cultivated population of tench (Tinca tinca (L.)) originating from Galicia in Poland, is also present in Porla. Its method of cultivation is the same as for carp and the tench use the same ponds at the same time as the carp. However, tench fingerlings cannot withstand wintering over in spring water in indoor basins. The carp do not appear to have suffered any ill effects as the result of this simultaneous cultivation.
The first carp were stocked into natural waters in 1956. Initially the numbers stocked were only 20–400 individuals per year. The first crossbred carp were stocked in 1960. Since 1961, the numbers stocked have increased noticeably. In the best years, Porla has supplied about 16 000 juveniles per year for stocking purposes. The method of cultivation and weather conditions have combined to exaggerate the annual variations in numbers; in some years there were no juveniles at all available for stocking. This also illustrates the difficulties of cultivating carp in Finnish conditions. The Porla Fish Culture Station has supplied between the year 1956 and 1981 a total of 138 000 one-three year old individuals for stocking (Table 1), the main purpose of which has been to determine whether carp could be used in the management of eutrophicated waters.
Other fish culture stations supplied in 1979 27 500 one-summer to two-year old carp for stocking (Anon., 1980b) and in 1980 5 000 one and two-summer old carp (Eskelinen and Sumari, 1981; Westman et al., 1982; Westman and Tuunainen, 1982).
The majority of the stockings were made in southern Finland and the southernmost inland waters of central Finland (60–62°N). A few stockings were also made in the brackish bays (S °/00 3–5) on the coast of the Gulf of Finland. The northernmost carp stocking was done in the Kajaani district (c 64°N) and the northernmost crossbred carp stockings in the lijoki River water system (65–66°N), in Lake Kemijarvi (66°30'N) and the southern part of the municipality of Inari (c 68°N) (Map 1).
In order to study the profitability of carp stocking, some of the stocked juveniles were tagged. By the end of 1981 some 13 000 two-year and older carp had been individually marked with metal wire Carlin tags and more recently with the plastic wire form of Carlin tags. Over 1 200 of the tags have been returned. A summary report has been made of all taggings done up to 1973 with spring-stocked carp of at least two years of age (Sormunen et al., 1976).
In inland waters the rate of return of carp tags has varied between 0 and 32 percent, which in terms of a catch means 0–336 kg/1 000 stocked fish. The best result in brackish water has been 40 percent, or 257 kg/1 000 stocked juveniles. Of the 18 marked stockings, 12 had a rate of return of 10 percent or more, 10 stockings had a calculated catch of over 100 kg/1 000 stocked carps of these 10 stockings 7 had a catch of over 150 kg/1 000 stocked fish (Sormunen et al., 1976). Some of the results of tagged stockings are shown in Tables II–IV.
However, as 1 000 20–21 cm long carp weigh about 150 kg in the spring, and 1 000 23-cm long carp weigh about 200 kg, it seems that the catch calculated from returned tags often does not equal even the total weight of the juveniles stocked.
It is often suspected that the Carlin tags work loose and drop off the carp, perhaps in large numbers, and for this reason the tag return gives too pessimistic a picture of the success of stocking (Sormunen and Kajosaari, 1975). This view is supported by the fact that the largest carp whose tag was returned weighed 5.1 kg and only a few tagged carp of over 3 kg have been reported, while untagged carp of over 6 kg are being caught constantly as well as a number of 10-kg carp, including the current Finnish record carp of 11.9 kg (Anon., 1981). In addition, in some lakes in which only tagged carp have been stocked, carp with no tags have been caught. These often have clear scars where the tag should be. The tag could come loose if the fish catches it on vegetation or a fish trap and pulls itself free or the tag may be rejected by the body of the fish.
Along with tag loss the results of tagging trials are affected by the willingness of fishermen to return the tags. It has been estimated that the number of unreturned tags varies between 10 and 70 percent of the number of returned tags depending on species and fishing ground. The results from tagging carp are also affected by the fact that the behaviour of the fish is not well known to Finnish fishermen who rarely catch it.
Although it is likely that carp spawn in some of the waters in which they are stocked the offspring would appear unable to survive the first winter. There has not been a single observed instance of the successful self reproduction of carp in Finland.
The growth of carp in eutrophicated waters is good compared with other fish. The additional growth of two-year old stocked juveniles, which weigh about 200 g at stocking, is often over 1 000 g during the first year.
After stocking, carp may be fished for a long time. Some tagged carp have been caught ten years after stocking. In one instance carp (untagged) have been caught 21 years after stocking (Kajosaari, 1980).
All in all, it is an appreciable benefit that once stocked, carp remain in the waters for a long time without forming a stunted population.
Carp stockings are threatened by the same enemies as other fish. The worst predator is pike; several carp tags have been found in pike stomachs. In practice, the only predator of carp over 300 g is Man. No predator, disease or parasite specific to carp alone has been observed. The introduction of carp to Finland has not introduced any new fish parasites or diseases.
Carp swim in schools, particularly during the fingerling stage. A frequent observation has also been of schools of carp at the surface of the water, sexually mature fish basking in the sun. In the fish culture stations, however, large carp appear to be content alone or in pairs during the summer.
Several of the Finnish manuals have stated that carp hibernate in the winter, remaining motionless on the bottom or even dug into the silt. As far as we know, this behaviour has not actually been observed. In the Porla Fish Culture Station, carp remain in motion throughout the winter, even in ponds which have frozen over. During the winter the fish collect in very dense schools and move slowly all the time even though the school as a whole may remain in the same place. Sometimes the eddies caused by such schools melt the ice above them completely. In natural waters, large carp have been caught by stationary traps below the ice, which also means they must be moving about in the winter. There are no observations on the behaviour of fingerlings in natural waters.
The diet of carp is broad and they are capable of efficient feeding even under competitive conditions. Carp thrive even in those waters with large, slow-growing bream (Abramis brama (L.)) and roach (Rutilus rutilus (L.)) populations where there is great competition for food. Carp is able to utilize the larger molluscs and to syphon food animals from deeper in the bottom than any of our domestic fish species. It prefers to search for food in warm, shallow waters, among vegetation, and for this reason seeks the littoral and when stocked in brackish water, shallow inlets. Carp has not been observed as having an impact on vegetation in any of the waters in which it has been stocked.
Nowhere in Finland has carp displaced another species of fish; of course, the number of juveniles stocked has not in any case been large enough to cause such displacement. In oligotrophic waters, the growth of carp has been slow in some cases and as a rule becomes slower after sexual maturity. There have been no observations of stocked populations forming stunted populations.
One year old fingerlings have not been tagged as even during a good growing season, these are so small that the added stress caused by a Carlin tag would undoubtedly have proved fatal. Untagged, one-year old carp have been stocked in tens of thousands in many places (Table 1, Map 1). For the moment there is no confirmed data on whether or not fish from these stocking have survived to reach fishing size.
As expected, the tagging trials have shown that the larger the average size of the fish, the better the average rate of tag return. The results for stocked juveniles under 20 cm length have been below 100 kg/1 000 stocked individuals. The poor results may be due to stress and related phenomena caused by the tags themselves, predators and winter deaths, all of which most strongly affect the smaller individuals. This is supported by the comparative stocking study carried out by the authors on marked carp juveniles of the same age, but different size, in a lake in southern Finland (Lake Valkeajarvi, c. 61°N). Two different size classes (average lengths 14 and 21 cm) of two-year old carp were stocked in the lake. There were otherwise no differences between the two classes. After three summers, the return of 14 cm juvenile tags was 1.1 percent, and that of 21 cm juveniles 11.1 percent. On the basis of some findings, it appears that some of the under 14 cm fish are not able to grow enough to withstand the next winter and some of them are caught by predators, usually pike (Esox lucius L.). The rate of return in both cases was affected by the Carlin tags themselves. The tags' slow growth decrease resistence to infection and attract predators because of their visibility.
After size at stocking the most important factor in the success and growth of carps is the biotic potential of the water stocked, at least in southern and central Finland. The best results have been obtained in relatively eutrophicated lakes, with lush aquatic vegetation and bottom fauna. In at least one instance, the lake in question was one in which bream remained undersized because of competition for food but in which the carp nonetheless thrived. On the other hand, some data also exists on instances of lakes with minimal biotic potential in which carp grew to a relatively large size (Seppovaara, 1965; Kajosaari, 1980).
The northernmost limit for successful carp stockings has proved difficult to define. Carp appeared to do sufficiently well in Lake Sokajarvi (64°15'N) and a few of the best results were obtained near Kuopio (63°N).
There is no fish which can compare with carp for size and strength, behaviour and caution in the natural waters in Finland. The closest comparison is with bream (Abramis brama) but bream weighing over 2 kg are rare. In Finland, however, fishermen are not accustomed to catching carp and no fishing gear designed for them is in use. Furthermore, the fishermen lack knowledge of the habits and behaviour of carp and do not know when or where it is best to fish for this species. In many of the stocked waters, most of the carp probably remain uncaught and die of old age.
On the basis of the tag return data, carp have been caught by rod and line with worms as bait, in trawl lines, fyke nets, fish traps and various size gill nets. Usually the nets have had a mesh which is too small for carp, since people are used to catching pike, pike perch (Stizostedion lucioperca (L.)) and small fish. The most effective have been wide-mesh trammel nets. These have been used for a long time in areas where there are fast-growing bream. Another particularly effective method has been the old fishing trick of torch fishing at night in shallow water with artificial light and a multipronged, long-handled, fishing spear. The largest carp caught so far in natural waters in Finland weighed 11.9 kg and was caught with a fishing spear (Anon., 1981). However, torch fishing is prohibited in many places.
Carp generally has a rather high value as a game fish. The reason for this is the large size attained: large individual fish have a recreational value, which does not depend very much on the food value of the catch. The rarity of the species increases the significance of the catch. The largest carp caught are usually published in the popular press. However, organized sportsfishing specifically for carp is very rare in Finland. More carp stockings have been requested in almost every body of water in which trial stockings have produced large-size game fish.
The appreciation of carp as food is very variable. It should be pointed out that in Finland carp is not available as food even as an import item, so that methods for its preparation and consumption are unknown. In warm waters, the flesh of carp, like that of all cyprinid fish, may take on an unpleasant flavour but the poor reputation of carp in Finland comes from fish caught in polluted waters in the summer or from small-sized, newly stocked individuals. The taste of individual carp of 1 kg caught during the cold season or kept in fish pens in fresh, clean waters, has been described as good or even excellent. Usually the flesh of carp weighing several kilos is reddish. The taste of properly treated carp is praised no matter how the fish is prepared and served. Since large-size food fish are valued in Finland, we expect interest in carp to increase considerably. For the moment, carp is not commercially available.
On the basis of the tagging trials carried out so far, it would appear that the value of the catch of carp is only in rare cases enough to cover the costs of stocking and fishing. Even though the true catch might be almost double that calculated on the basis of the returned tags, carp stocking in Finland has been either run at a loss or in the best cases at a very small profit, because Finnish fishermen are not used to fishing for carp. The development of more versatile catching methods, increased carp fishing and directing fishing at more economic size-classes, could combine to increase the catch from carp stockings.
As Sormunen and Kajosaari (1975) have pointed out, the results of stocking with carp or those of any other stocking for that matter, cannot be judged solely on the basis of how many of the stocked fish are actually caught. In evaluating the results, all factors should be considered, including the extent to which stocking has improved fishing and recovery for all species in a fish community, the profitability of fishing and its recreational benefit.
Carp appears to be comparable to salmonids as “prize fish”. The catch of an exceptional individual weighing several kilogrammes increases interest in the management of fishing waters as well as fishing in general, so that other fish are more efficiently utilized and the value of all fishing as a whole increases.
In some cases the catch appears to have influenced fishing habits very quickly. For example, at Lake Valkjarvi, formerly ordinary nets with a mesh size of 45–50 mm were in general use; but since carp were stocked, the use of 70–80 mm mesh trammel nets is more common.
Carp have not been observed to affect other fish, although they can be considered as competing with other bottom-feeding species. Equally, carp have not been observed to affect aquatic vegetation in the waters in which it has been stocked.
No observed new disease or parasite has been observed as a result of the importation of carp into Finland, neither have cultivated or stocked carp been observed to carry or spread any harmful disease.
The carp appears to occupy an otherwise free ecological niche. Its most likely competitors are the other cyprinid fish such as bream, white bream (Blicca bjoerkna (L.)), crucian carp (Carassius carassius (L.)), ide (Leuciscus idus (L.)), roach (Rutilus rutilus (L.)) and rudd (Scardinius erythrophthalmus (L.)). Of these, only bream and, to some extent, ide have any value as a catch.
Carp does not appear to have undergone any changes for the worse in its new environment but the species has developed during the 30 years it has been cultivated in Finland in that it is better able to tolerate cold water.
The data collected on carp in Finland has provided the basis for the following conclusions and recommendations:
Carp stockings have given economically significant results only in rare cases. This is mainly due to the unfamiliarity of fishermen with the behaviour of the species: they do not know where and when they should fish for carp. In Finland there is no tradition of fishing for fish like carp so the gear used is rarely suitable for catching it.
Carp evidently does not reproduce successfully under natural conditions. Stockings have succeeded in many different types of waters, even in northern Finland. The best results have been obtained in eutrophicated lakes. Because carp support waters with rather little dissolved oxygen they seem to be of significance particularly in the management of lakes in southern Finland which are already eutrophicated or in the process of eutrophication. The effective utilization of these waters has proved to be a problem because of the lack of domestic fish species suitable for stocking into these waters.
On the basis of 30 years experience with carp in Finland, it would appear that carp has not caused any observed damage in the waters stocked to other fish species, to vegetation or to the ecosystem in general. The species also does not appear to be a serious competitor of domestic fish species or to replace or hybridize with them.
No dangerous fish diseases or parasites have been observed in carp, neither has it been observed to carry or spread such or to serve as an intermediate host for them.
Carp does not appear to have undergone any changes since introduction except that the Finnish population is perhaps more cold-tolerant.
Carp stockings have achieved their intended objectives to some extent; although lack of interest in catching carp limits the success.
There is reason to continue carp stockings, especially in eutrophicated or eutrophicating lakes. Juveniles for stocking should be over 20 cm in length; and stocking should be made in early summer.
Fishing for carp should be increased in the waters in which it is stocked; fishing should be aimed at that size-class which gives the best economic result, yield, and value of catch; and fishing methods should be developed and made more versatile. This requires that research and trial stockings be emphasized and strengthened and that more information be given to fishermen on the behaviour and life-cycle of carp, their growth and mortality, and the results of studies and experiments on catching carp.
Methods for the controlled reproduction of carp and the cultivation of juveniles for stocking purposes should be developed so that the short growing season in Finland may be utilized to the full. New cultivation methods, such as the use of the warm effluents of power plants, should be developed.
Eskelinen, U. and O. Sumari, 1981 Kalanviljely Suomessa vuonna 1980. Suom.Kalankasvattaja, 1981(4):21–3
Huet, M., 1971 Textbook of fish culture, breeding and cultivation of fish. Farnham, Surrey, Fishing News (Books) Ltd., 454 p.
Ilmarinen, P., 1982 Porlan kalanviljelylaitoksen toiminnan kehittamisesta. 5p. (mimeo)
Kajosaari, H., 1959 Karpinpoikasia Neuvostoliitosta. Suom. Kalestuslehti, 66(1): 21–2
Kajosaari, H., 1962 Ulkolaisten kalalajien kasvatuskokeilut, valiaikatietoja. Metsastys Kalastus, 51(4):139–42
Kajosaari, H., 1966 Karppikokeista myonteisia tuloksia. Metsastys Kalastus, 55(7–8):331–3
Kajosaari, H., 1980 Karpin viljely ja istutus. Suom.Kalastuslehti, 87(3):74–6
Kalataloussaatio (Fisheries Foundation), 1961–78 Toimintakertomukset vuosilta 1960–77 (mimeo reports)
Kirpitschnikov, V.S., 1957 Karpfenzucht im Norden der UdSSR. Dtsch.Fischereiztg., 4:213–6
Malmgren, A.J., 1883 Lausunto, jonka keinotekoisen kalankasvatuksen soveliaisuudesta Suomeen on keisarillisen senatin maanviljelystoimikuntaan antanut And. Joh. Malmgren, kalastuksen tarkastaja, ylim. prof. ym. Hameenlinna, Hamalaisen osakeyhtio, 86 p.
Saari, L., 1937 Karpin istutusta kokeiltu Keski-Suomessa. Suom.Kalastuslehti, 44(9):192
Saari, L., 1939 Karppi ei ole kutenut Mantassa. Suom. Kalastuslehti, 46(1):22
Sandman, J.A., 1892 Karpin kasvattamisesta pohjoismaissa. Suom.Kalastuslehti, 1(5):69–76
Seppovaara, O., 1965 Karpista. Urheilukalastaja, 1965 (4):21–4
Sormunen, T. and H. Kajosaari, 1975 Karpin viljely ja istutus Suomessa. In Eramaailma, edited by H. Sarrala. Hameenlinna, Karisto, pp. 41–50
Sormunen, T. et al., 1976 Yhdistelma Kalataloussaation suorittamien kalamerkintojen merkkipalautusten yhteydessa saaduista saalistiedoista. Kalataloussaation monist.julk., 55:1–468
Westman, K. and P. Tuunainen, 1984 A review of fish and crayfish introductions made in Finland. EIFAC Tech.Pap., (42) Vol.2:436–48
Westman, K. et al., 1984 A review of fishing stockings in Finland. EIFAC Tech. Pap., (42)Vol. 1:252–68
Wuorentaus, Y., 1938 Ulkomaisten kalaiajien koteuttamisyrityksia. Luonnon Ystava, 42(3):87–92
Anon., 1980 Karppiennatys kasvoi kilolla. Suom.Kalastuslehti, 87(5):151
Anon., 1980a Kalanviljely vuonna 1979. Suom.Kalatalous, 49:1–3
Anon., 1980b Riista- ja kalatalouden tutkimuslaitoksen toimintakertomus vuodelta 1979. 144 p. + 6 tables (mimeo)
Anon. 1981 Karppiennatys parani. Suom.Kalastuslehti, 88(8):251
Anon., 1982 Riista- ja kalatalouden tutkimuslaitoksen kalantutkimusosaston tutkimus-, palvelu-, tiedotus- ja julkaisutoiminta vuonna 1980. (Research, service and information work, and publications of the Fisheries Division of the Finnish Game and Fisheries Research Institute in 1980.) Riista- ja kalatalouden tutkimuslaitos kalantutkimusosasto tiedonantoja, 19:1–118
Table 1 The number of various aged carp and crossbred carp supplied by the Porla Fish Culture Station for stocking purposes in the years 1956–81 (Kajosaari, personal communication, Fisheries Foundation Reports 1961–78; Anon., 1979, 1980c, 1982)
| Year | one-year | 2-summer | 2-year | 3-summer | 3-year | 2–4 year? | Total | ||||||||
| 1956 | - | - | - | - | 160 | - | - | - | - | 160 | |||||
| 1957 | - | - | - | - | - | - | - | 20 | - | 20 | |||||
| 1958 | - | - | - | - | - | - | - | - | 400 | 400 | |||||
| 1959 | - | - | - | - | - | - | - | - | 200 | 200 | |||||
| 1960 | - | - | - | - | 225 | - | - | 125 | - | 350 | |||||
| 1961 | 5 900 | - | - | - | - | - | - | - | - | 5 900 | |||||
| 1962 | 9 250 | - | - | - | - | - | - | - | - | 9 250 | |||||
| 1963 | - | - | - | - | - | - | - | - | - | 0 | |||||
| 1964 | 4 900 | ** | - | - | - | - | - | - | - | - | 4 900 | ||||
| 1965 | 3 700 | ** | - | - | - | 220 | ** | - | - | - | - | 3 920 | |||
| 1966 | 4 900 | ** | - | - | - | - | - | - | - | - | 4 900 | ||||
| 1967 | 325 | 7 450 | * | - | - | 150 | 520 | * | - | - | - | 8 445 | |||
| 1968 | 6 880 | - | - | - | 750 | 1 020 | * | - | - | - | 8 650 | ||||
| 1969 | - | - | - | - | 1 490 | 420 | * | - | - | - | 1 910 | ||||
| 1970 | 14 040 | - | 30 | 20 | * | 850 | - | - | - | - | 14 940 | ||||
| 1971 | 2 200 | - | 275 | - | 900 | 1 770 | * | 1 450 | - | - | 6 595 | ||||
| 1972 | 500 | - | - | - | 760 | 970 | - | 600 | - | 2 830 | |||||
| 1973 | 10 770 | - | 2 100 | 1 070 | * | 2 070 | - | - | - | - | 16 010 | ||||
| 1974 | 8 115 | - | 1 140 | - | 2 830 | 310 | * | - | - | - | 12 395 | ||||
| 1975 | 80 | - | 325 | - | 2 190 | 1 785 | * | 830 | - | - | 5 210 | ||||
| 1976 | 6 130 | - | 1 920 | - | - | 1 445 | * | - | 490 | - | 9 985 | ||||
| 1977 | 2 900 | - | 1 640 | - | 1 220 | - | - | - | - | 5 760 | |||||
| 1978 | - | - | - | - | - | - | - | - | - | 0 | |||||
| 1979 | 2 880 | - | - | - | 630 | - | - | - | - | 3 510 | |||||
| 1980 | 3 500 | - | 1 120 | - | 2 050 | - | - | - | - | 6 640 | |||||
| 1981 | 2 300 | - | 500 | - | 940 | - | - | - | - | 3 740 | |||||
| 137 650 | |||||||||||||||
* crossbred carp
** exact number of crossbred carp unknown
Table 2 Carp stocking in brackish water: Helsinki, Suomenlinna - Kaivopuisto (60°10'N) 10/6/68 - 500 individuals stocked, average length 23.5 cm, average weight 247 g. Return result 257 kg/1 000 stocked (Sormunen et al., 1976)
| Catch year | Catch | Average weight | Largest individual | ||
| Ind. | % | kg | g | g | |
| 1 = 1968 | 172 | 34.4 | 104 | 602 | 1 400 |
| 2 = 1969 | 22 | 4.4 | 20 | 894 | 1 600 |
| 3 = 1970 | 4 | 0.8 | 5 | 1 325 | 2 100 |
| TOTAL | 198 | 39.6 | 129 | 673 | |
Table 3 Carp stocking in a lake in southern Finland: Tuusula, Lake Tuusulanjarvi (60°20'N) 1/6/67 - 50 individuals stocked, average length 26.6 cm, average weight 300 g. Return result 336 kg/1 000 stocked (Sormunen et al., 1976)
| Catch year | Catch | Average weight | Largest individual | ||
| Ind. | % | kg | g | g | |
| 1 = 1967 | 13 | 26.0 | 9 | 690 | 1 100 |
| 2 = 1968 | 0 | ||||
| 3 = 1969 | 1 | 2.0 | 2 | (2 000) | (2 000) |
| 4 = 1970 | 1 | 2.0 | 2 | (2 400) | (2 400) |
| 5 = 1971 | 1 | 2.0 | 3 | (3 450) | (3 450) |
| TOTAL | 16 | 32.0 | 17 | 1 052 | |
Table 4 Carp stocking in a lake in central Finland: Siilinjarvi, Lake Sulkavanjarvi (63°10'N) 10/6/70 - 200 individuals stocked, average length 20.9cm. Return result 230 kg/1 000 stocked fingerlings (Sormunen et al., 1976)
| Catch year | Catch | Average weight | Largest individual | ||
| Ind. | % | kg | g | g | |
| 1 = 1970 | 17 | 8.5 | 13 | 757 | 1 300 |
| 2 = 1971 | 18 | 9.0 | 18 | 1 006 | 1 500 |
| 3 = 1972 | 7 | 3.5 | 12 | 1 689 | 2 200 |
| 4 = 1973 | 1 | 0.5 | 3 | (3 150) | (3 150) |
| TOTAL | 43 | 21.5 | 46 | 1 076 | |
Map 1.
Stockings of carp in Finland
from the Porla Fish Culture
Station in 1956 – 1981.
Not all stocking places
south to the broken line
are marked.
