M. von Lukowicz and Chr. Proske
Bavarian State Institute for Fishery Starnberg, Federal Republic of Germany
ABSTRACT
Although tench (Tinca tinca Linné) is an important pond fish in Middle-Europe and the interest in its cultivation is steadily increasing, the knowledge of reproduction and fry rearing is rather poor. Reproduction of tench mostly takes place in carp ponds in a natural way and fry and fingerlings are more or less a by-product in carp farming. Artificial propagation is still in the stage of experiment and has not yet been fully developed.
Purpose of this paper is to give a survey of production and reproduction of tench as far as information is available from literature. Progress in tench culture can only be achieved if intensive scientific and practical work is carried out on this subject in future.
RESUME
La tanche (Tinca tinca L.) joue un rôle de plus en plus important en Europe Centrale. Cependant les méthodes de reproduction et d'alevinage sont mal connues. La reproduction s'effectue généralement dans les étangs à carpes et ne fait pas l'object d'une attention spéciale, l'alevinage se faisant de façon naturelle. La reproduction artificielle se trouve dans un stade expérimental.
Sur la base des publications qui ont vu le jour, ce rapport présente quelques données relatives à la biologie, la reproduction et la production de la tanche. Ce n'est que par une conjugaison des efforts sur le plan scientifique et pratique que l'on avancera ce domaine.
Since the beginning of this century the tench (Tinca tinca Linné) is an important pond fish in Middle-Europe. Recently there has been a decline of tench production (Wunder, 1958; Evert, 1974). In the following present knowledge of tench rearing and production is described briefly on the basis of literature. Progress in tench management depends on the improvement of genetic material and reproduction technology. Therefore the basic features of breeding and reproduction of this species are reviewed.
The tench is wide-spread in Europe and can be found also in the near orient and western Siberia (Anwand, 1965). It was also introduced in Africa, Australia, South-East-Asia and North-America where it has partly become an endemic species.
Tench is an eurytherm species with a less specific temperature demand than that of common carp (Cyprinus carpio L.). Thus it exists at altitudes of 1600 m above sea level and on the other hand it can stand water temperatures of more than 35°C. Also the water quality requirements are low. The pH of the water should be between 6.5 and 8.0 but lethal values are below 5.0 to 4.5 and above 10.8. Some authors point out that tench preferes acid water for reproduction and that spawning is hindered in waters having been fertilized with big quantities of lime (Wunder, 1958). Detailed investigations in this respect are lacking.
Furthermore a very low demand for oxygen is reported. At a temperature of 0°C tench of marketable size consumed 8.6 mg 02/kg × h and 143.3 mg 02/kg × h at about 25°C (Koch et al., 1976). The level of metabolism is not mentioned. The endurance by tench of oxygen deficiency during transport and in storage ponds is well known. But in summer it can be sensitive to lack of oxygen and it hardly supports to be fished out from ponds at high temperatures.
The natural food sources for adult tench are the same as for carp. Common supplementary feeds are also taken, but the food conversion rate is less favourable than in carp (Heuschmann, 1939). There are no recent investigations on the demand of nutrients.
Tench is sensitive to skin damage with subsequent infection of fungi and to affections by parasites. Frequently Costia, Chilodonella and Ichthyophthirius are to be observed. Fry of tench is susceptible to Dactylogyrus. The formerly feared Ergasilus can be controlled at present by a treatment with Masoten. Important diseases of tench are Trypanoplasmosis and Branchiomycosis. Furthermore tench is known as carrier of the agents of Spring Viraemia and Erythrodermatitis.
In general tench is considered to grow slowly, the average weight being 5 – 15 g after the first, 50 – 100 g after the second and 250 – 300 g after the third summer (Müller, 1961). But already 60 years ago it was shown that by means of positive mass selection the growth can be improved considerably (Probst, 1937). The well known “Quolsdorf tench” reached a length of 17 cm in the first year, a weight of 250 g in the second and of 800 g in the third year (von Milkau, 1921). Recent experiments on tench breeding with application of modern methods of population genetics and hybridisation are not known. It has to be mentioned that there are differences in growth between male and female particularly when tench reaches maturity. Mann (1956) observed a 100% better growth of females as compared to males.
The reproduction of tench causes difficulties. The brood fish do not spawn in small ponds (Heuschmann, 1939). Small fry cannot be harvested from big ponds. Thus regular stocking measures are almost not possible. Furthermore the date of spawning is strongly dependent on climatic conditions. Spawning time can extend from May to August. A late spawning in summer means a short growing season for the fry which consequently cannot reach the wanted size in autumn.
Despite these disadvantages reproduction of tench mostly takes place in a natural way in carp ponds. It is more or less a by-production in carp farming, the success of which is unreliable and cannot be predicted. Therefore besides breeding measures aiming at high performance, methods of controlled propagation of tench have to be elaborated. The biological features have been known for long, but up to now a suitable and satisfactory bio-technique has not been developed.
It is not certain if common methods of stripping as applied with other cyprinids are successful with tench (Probst, 1937). Females usually discharge the eggs in portions. A great part is retained and later resorbed. Evert (1974) experienced that 41% of the females can be stripped in a stage of high ripeness without any application of pituitary. Hypophysation or the use of mammalian hormones mostly did not stimulate the maturation of females or of males.
During fertilisation of the eggs the use of solution of 10 g sodium chloride and 10 g urea per 1 l of water gives a higher fertilisation rate with a range between 10 and 90% (Evert, 1974). The eggs are very sticky and clot together if not treated with Tannin. Stickiness is less pronounced with overripe eggs. The most favourable temperature for incubation is 25° C. Hatching takes place after 36 – 43 d° (day degrees). Lower temperatures do not only delay the embryonal development but also increase the number of d° (20° C: 60 – 70 d°).
Remarkable experiences in the artificial propagation of tench have been made in Hungary (Horvath, 1979; personal communication): The ripe spawners receive one intraperitoneal injection of hypophysis extract (4 – 5 mg per fish) and are set into a basin with an artificial spawning substratum. After having started with the mating behaviour (after about 18 h at 24° C) female and male are stripped for the first time. The females give about 100 g of eggs, of which 70% are ripe; 1 – 2 h later a second portion of eggs (about 50 g) can be gained. The male produces only little milt and 2 – 3 males must be taken for 1 female. Sometimes the testes have to be passed through a sieve. The eggs are fertilized with the dry method and a solution of 3 g urea per 1 l of water is added for 1 – 1.5 h. The fertilisation rate is above 80%. The stickiness of the eggs is less pronounced than with carp eggs and treatment with tannic acid is not necessary. Incubation takes place in glass jars (3 d, 24° C).
Just hatched fry of tench are very small (Lo = 3.8 – 4.3 mm), not pigmented and sensitive to light. The larvae are motile between 20° and 25° C. Above and below this temperature range they do not move and are lying on the aquarium bottom (Evert. 1974).
Feeding starts on the 3rd to the 6th day, depending on the water temperature, when most of the yolk sac has been resorbed. The first food is small zooplankton (crustaceans, rotifers). but also Microcystis is accepted (Evert, 1974). From 10 mm length and onwards the fry are no longer vulnerable to predatory plankton like copepodes.
Evert (1974) found the following growth figures after hatching:
| 7 days : | 5.5 – 5.8 mm |
| 12 days : | 5.8 – 6.3 mm |
| 25 days : | 10.0 – 14.7 mm |
In his experiments first-feeding with artificial food was possible. From the 5th day the larvae took up food from the water and the next days also from the bottom. But fed on artificial food the fish grew slowly reaching an average length of 6.1 mm after 20 days.
In Hungary the hatched fry are kept in aquaria for 6 days and egg yolk is applied as a first food during one day only. After that the fry are stocked into small ponds at a density of 100 000 –600 000/ha.
In practice tench is produced alsmost exclusively in polyculture with carp. Tench monoculture does not give satisfactory yields per unit of area - at least not using common supplementary feedstuffs. Therefore this kind of tench production is considered to be uneconomic. No experiments of feeding with pelleted feed (complete feed mixture) are published. But our observations showed indeed that tench readily take up dry pellets from self feeders. This was confirmed by other experiments (Bohl, 1974, personal communication).
Formerly published production figures for tench relate to a low production level (about 200 kg/ha) and are not applicable anymore, Schaeperclaus (1967) recommends to stock tench in an amount of 10 – 20% of the carp stock (specimen). A higher percentage would be detrimental to the total yield. According to our experiences the share of tench can be higher in ponds with ample aquatic vegetation.
With the genetic material available nowadays in tench, a three year production period is required to achieve a marketable individual size. It is strongly recommended to separate males and females in the third year, because strong competition in feeding can arise from uncontrolled reproduction in ponds.
In some bavarian pond farms tench is produced as a main fish (more than 50% of the total fish stock) in polyculture with grasscarp (Ctenopharyngodon idella), pike perch (Stizostedion lucioperca), carp and other cyprinids. Figures of yields are not yet available.
From the fact that there is only little information concerning production and reproduction of tench it is obvious that intensive scientific and practical work has to be carried out on this subject in future.
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