Optimalisering van de groei bij de karper (Cyprinus carpio L.) : een op de visteelt gericht onderzoek

In course of time carp culture - in Europe already practiced since the Middle Ages - has been subjected to different patterns of intensification e.g. fertilization of ponds and supplementary feeding. Mechanisation in pond farm management has also proved to be important.

The aim of these measures has always been to increase the ratio of fish production to financial and/or labour investment.

The experiments reported in this thesis also aimed to investigate the possibilities of intensification of carp culture using running water systems. Attention has been paid to the different stages of carp culture, e.g. reproduction, fry-raising and the rearing of larger carp.

In chapter I different patterns of intensification in present day pond farm management has been briefly described.

In chapter II the experimental unit, the pelleted food, the methods and calculations, employed in this research have been described.

Experiments concerning induced reproduction using carp pituitaries have been dealt with in chapter III. The technique of hypophysation has proved to be a very reliable addition to normal procedures for reproduction of carp in ponds (fig. III). Furthermore it is possible to induce reproduction of carp independent of the season with very good results. For this purpose carp have been kept in warm water (23° C) before hypophysation: this treatment subjects the fish to a certain amount of heat (in ° days). The characteristic of high temperature treament which is essential for successful induction of spawning is the actual water temperature.

During this time no influence of light has been observed (table V).

The relationship between temperature and amount of heat followed the same pattern as the temperature dependancy of metabolic rate as described by Ege and Krogh (1914) and by Winberg (1956).

In chapter IV a method has been reported for raising carp fry under artificial conditions in a hatchery. Carp fry kept in aquaria with running water of 23° C have been fed larvae of Artemia salina until they attained a weight of 70 mg. Fry over this weight accepted commercial pelleted food. Fingerlings cultured in this way have proved to be good stocking material for ponds and for other production units.

Experiments in raising larger carp have been reported in chapter V. This stage is of great economic importance in carp culture because it takes a long time and needs large amounts of food. Therefore some essential characteristics of growing carp have been studied more thoroughly.

The first section of this chapter deals with growth rate of carp. At 23° C experiments have been carried out in order to determine the relationship between food ration, specific growth rate and food conversion using carp of different weights (1.5-10, 30-90 and 100-1,000 gram). At 17° C the same relationship have been determined using carp of 30 gram (fig. V and VI).

In the graph relating the feeding level and the specific growth rate (fig. VI) the "geometrical optimal feeding level" ("G.O.-level") has been determined by constructing the tangent to the curve from the origin. From the point of view of fish production other criteria relating final cost price are important; a high, but not maximal growth rate with a worse but still acceptable food conversion, might be preferred. These high feeding levels must be harmless to the fish. Therefore a "productive optimal feeding level" ("P.O.-level") has been approximated for carp of several sizes.

As a result of the analyses of body constituents and calorific content of carp kept at different feeding levels (table XIV and XVI) it has been proved that when feeding a "G.O.-level" the specific growth rate based on fresh weight was as high as based on dry weight and on calorific value (fig. VIII). The optimum between gross conversion efficiency (K ₁ ) and feeding levels has been found at the "G.O.-level". This optimum was the same for K ₁ expressed in fresh weight, dry weight or calorific value (fig. IV and XI).

As a consequence of this the work of Paloheimo and Dickie (1966b) has been criticized. linear relationship between log K ₁ and the feeding level is given by these authors. It has been shown here that this relationship is only valid to the range of feeding levels above the "G.O.-level". Furthermore it has been shown that K ₁ was negatively influenced by increasing weight (fig. X). An influence of temperature on K ₁ could also be established (fig. XI).

In the second section of this chapter the oxygen consumption of fasting and growing carp of different weights has been investigated. For fasting carp the relationship between oxygen consumption (T, in ml/h) and fish weight (W. in grams) could be described by the equation: T = 0.372 W ^0.816(fig. XIII).

Measurements at 17° C showed that the influence of temperature on oxygen consumption was similar to that found by Ege and Krogh (1914).

For growing carp the relationship between oxygen consumption (ml/kg0.8/h) and feeding level (% of body weight per day) has been established. With increasing feeding levels oxygen consumption increased. However, no further increase of oxygen consumption could be demonstrated at levels above the "P.O.-level" (fig. XIV). For "P.O.- level" the relationship between oxygen consumption (T, in ml/h) and fish weight (W, in grams) could be described by the equation: T = 0.861 W ^0.776(fig. XVI).

At "P.O.-levels" the amount of oxygen consumed for each kg of food was 147 l, independent of fish weight and water temperature (table XXIV). Based on these data a simple equation could be derived relating in a running water system the oxygen content of the inflowing water (O _i , in ml/l), the oxygen content of the water at discharge (O _u , in ml/l), and the flow rate (D, in l/sec) to the amount of food per day in kg:

(O _i - O _u ). 86.4/147 . D = kg of food per day.

The value for O _u in the equation could be fixed at 2.1 ml/l as has been shown by the relationship between food conversion and oxygen content of the water (fig. XV).

Based on the results obtained in the first and second section, in the third section of this chapter both gross and net efficiencies for maintenance and production have been calculated. Carp requires 171.6 kcal gross energy/kg ^0.8/week for maintenance. The utilization of the gross energy for maintenance was found to be 45.2% efficient. The percentage of metabolizable energy (% ME) of the rations fed and eaten has been determined by measuring the energy content of the food, of the depositions during growth and of the heat production, the latter being calculated from the oxygen consumption. Both % ME and gross production efficiency decreased with increasing feeding levels, the respective values varying between 23.8-56.8% and 15.3-44.1% (fig. XVIII). The amount of ME required for maintenance amounted to 110.4 kcal/kg ^0.8/week. The efficiency of the utilization of the ME above maintenance proved to be almost the same for alle, feeding levels used and varied between 85.6-89.4% (fig. XIX).

The content of ME of the food dry matter originated from these experiments were much lower than those reported in the literature for fish fed natural food. However, most of those data in the literature have been calculated by measuring the calorific value of the food ration and of the feacal material. The analysis of the detailed study of Kelso (1972) suggested that a large error is introduced by this method for calculating the ME content for the consumed food (table XXVII and XXVIII).

In chapter VI methods have been described by which the results obtained by this study can be put into practice in carp culture. Integration of the above mentioned nursery procedures in hatcheries with cage culture of carp in warm water discharges and with conventional pond farming appears to be an excellent way to improve the efficiency and intensification of carp culture.