B. Ržaničanin
Faculty of Agricultural Sciences, University of Zagreb, Zagreb, Yugoslavia
ABSTRACT
Grass carp and silver carp fry were reared in small (100–400 m2) ponds with a survival rate of 53 and 72%. In big ponds (2–3 ha) the fry of grass carp, silver carp and bighead carp survived at a rate of 42, 63 and 60% respectively.
The culture methods are summarily described.
RESUME
Les carps chinoises élevées en petits étangs (100–400 m2) ont eu un taux de survie de respectivement 53 p.c. en ce qui concerne la carpe herbivore et de 72 p.c. en ce qui concerne la carpe argentée. Elevées en grands étangs (2–3 ha), leur taux de survie était de 42, 63 et 60 p.c. respectivement pour les carpes herbivores, les carpes argentées et les carpes marbrées.
Les techniques d'élevage sont sommairement décrites.
The production of herbivorous fish is increasing in our country every year, but the capacity of the existing fish ponds has not yet been fully utilized. The reason for that lies in the technology of fry/fingerlings production.
In order to improve the results the influence of the unfavourable environmental factors has to be diminished. These factors are particularly harmful to the youngest fish because they are most sensitive. On the basis of our own experience and that of others we succeeded in stabilizing and in gradually increasing the production of fry an fingerlings but it is still insufficient in comparison to the fish farmers' demand.
In the production we use small and big earthen ponds with various feeding and fertilizing systems. The common goal of the various methods is to secure fast growth and better survival, monitoring at the same time the production profitability.
In order to achieve the best conditions in the pond it must be previously dried up, with the grass cut, and then limed by 1–2 tons/ha taking into account the quality of soil and water.
The shape of the pond bottom should prevent the growth of the hard and sharp water weeds and provide the small draining canals enabling thus the easier fishing out later on. At the pond filling special care should be taken to prevent the entering of trash fish and their larvae.
The time when the ponds are filled with water is also of essential importance for fry rearing. The filling should take place 3 to at most 7 days before stocking of larvae. Earlier filling would cause the development of the harmful insect fauna and of zooplankton consisting of big Cladocera species mostly. However filling the pond 3–7 days in advance of stocking should secure the development of small species of zooplankton (Rotatoria and Copepoda larvae) which are proportionally suitable in size for tiny fry mouths. The development of the natural food and of its size plays an important role in fry and later on in fingerlings feeding. Depending on water temperature the fry start to take food between the 4th and the 6th day of life. At this time and during the subsequent days they need natural food of small size.
According to the experiments the survival of fry depends on water filtration; with filtrated water the survival rate was 53 per cent while in the objects without water filtration it was only 16 per cent.
The stocking density in the pond, the feeding rate and the eventual fertilization are the further measures. If the fish is fed and all intensified rearing measures are applied as well, the stocking density could be from 2 to 3 million/ha.
The growth rate and the survival of plant eating fish fry do not depend only upon the natural food but also upon the additional food. Reportedly feeding the fry soy bean meal and cereal wastes and grass carp Lemna sp. gave very good results.
The presented results were obtained on two types of ponds of different size which caused a certain variation in results. The preparation of the ponds was accomplished according to the previously mentioned procedure. The small ponds (100 m2 – 400 m2 in size) were stocked with 3 days old larvae, 3 days after being filled up with water; stocking density was 2.5 mil/ha. During the first 15 days the ponds were fertilized by complex fertilizer (NPK 17-8-9) 200 kg/ha in four doses. The additional feeding consisted of trout starter “trouvit”, while grass carp were fed Lemna in unlimited quantities. The initial meal was 2 kg for 100 000 fry and was fed during the day in four doses. The amount of food was gradually increased in relation to the fish appetite. Grass carp fed near the banks at the feeding places. The silver carp was given mashed food spread on the water surface during the first 15 days and dry starter later on. The natural food, especially the small forms of zooplankton and big quantity of phytoplankton were well developed.
During the second half of the rearing period we encountered the problem of the lack of oxygen in the water resulting from the big quantities of food used during the day.
Without aerators the feeding had to be stopped and after the 26 rearing days the ponds were fished out.
The length of reared fry was 2 to 4 cm; the survival rate was very high.
- 53 per cent for grass carp
- 72 per cent for silver carp
In the other ponds the rearing lasted for 30 days, the fry length being thus 2–5 cm. The percentage of caught fry was somewhat lower caused by the bigger pond surface (2–3 ha), more pronounced influence of external factors - frogs, for instance, which caused big losses.
Nevertheless the results obtained are satisfactory:
| grass carp | 42% (30–50%) |
| silver carp | 63% (35–70%) |
| bighead | 60% (40–65%) |
The results obtained during 1978 are satisfactory although each of the two methods has its drawbacks. Based upon the suggestions of some authors and on our own experience the following measures should be obeyed:
When the above measures are thoroughly and punctually carried out the results obtained will not be disappointing.
We have not much experience with rearing with covered facilities but the carried out experiments raise the hope for even better results. In the covered premises the basic factor that influences the fish organism at the most during the first days of life, the temperature fluctuation can be under control. This also holds for the frogs and tadpoles which cause, in our opinion, even more damages than parasites and diseases.
