Pike stocking material rearing
The abundance of various components of the fish stock depends on the conditions, what the environment of the inhabited reservoir creates for them throughout their lives. Happens often, that the potential opportunities for the development of species with a favorable environmental situation at their disposal - i.e. the abundance of food and space corresponding to the requirements of other biological properties - are limited by factors that prevent the successful course of natural reproduction. In such cases, you can keep the population at the level dictated by economic needs, if permanent replenishment of its number is applied with offspring raised in artificial conditions.
The rearing of pike stocking material is based on the methods used in trout and whitefish hatchery., however, it does not always give equally satisfactory results. The reason for the generally lower productivity is the high sensitivity of roe - and later also of juvenile forms - requiring extreme caution in all kinds of manipulations.. The fisheries literature brings constantly new suggestions for solving particular technical problems, which allows us to judge, that the search for the best method has not yet been completed.
Roe and dandelion are obtained from spawners caught with trap gears in early spring. To stockpile enough fish, fishing begins well before the date of natural spawning, in the period, when clusters begin to form near the banks, most often in the estuary zone of rivers and tributaries of the reservoir. One should pay attention to the numerical sex ratio, striving for more males, which produce very little dandelion during artificial spawning. Roes can be easily distinguished from males by the more pronounced convexity of the abdomen. It is generally believed, that individuals weighing 1-2 kg are the most suitable material. Larger females do have full-fledged eggs, but keeping them until they reach maturity and wiping them off is more difficult and laborious.
In natural environments, pike gonads - especially females - reach full maturity just before spawning begins. Therefore, earlier harvesting of spawners makes it necessary to keep them in such conditions, that would not interfere with the normal course of the maturation process. If the expected detention period is to be extended, it is advisable to use for this purpose - especially in the first phase - small lakeside rates. In the absence of them, satisfactory results can also be obtained using wooden cages placed on the flow and sheltered from the top, this is to reduce the activity of the fish, which, in full light, injure themselves hitting the walls. The permitted stocking density depends on the size of the fish kept. The spawners are in good condition with the stocking 20 pieces on 1 m3 of water was observed in a notch of dimensions 3,0 X 1,5 X 1 m (Genina i inni, 1958). If the fish have not been separated by sex before, they should be isolated several days before spawning is expected.
The gonad maturation process may be prolonged under unfavorable weather conditions or due to improper keeping of spawners. In carp breeding, in such cases the procedure of injecting fish with an emulsion is used, made from the pituitary glands of a carp or bream. This treatment, called hypophization, aims to enrich the body with hormones that accelerate the development of sex products. Wolf and Janovsky (1964) tried its effectiveness on pike and achieved successful results. Carp pituitary gland stored in acetone, injected - after grinding and mixing with physiological solution - into the abdominal cavity, delayed maturation spawns, in nine cases out of ten it had the desired effect without adversely affecting the further development of the eggs.
The maturity of the female is checked after lifting her, head up. If the roe starts to flow out on its own or with very light pressure on the abdomen, steps can be taken to obtain it and to fertilize it artificially. The "dry" method, proven for other species, has also found widespread use in pike hatchery.. The name comes from here, that the mixing of eggs and milk takes place without water, which, As you know, activates sperm for about two minutes and at the same time causes a quick closure of the tubule leading to the inside of the egg. So the idea is to gain the time needed to evenly distribute a small amount of milk throughout the volume of the spawned eggs.. This is one of the basic conditions for successful fertilization. Sperm activated by the presence of water move within a range of only 2-3 mm and a drop of milk placed on the surface of the egg layer can fertilize only these, which lie no more than twice the diameter of one grain from its edge, even though the number of sperm it contained would be enough to fertilize a liter of eggs (Lindroth, 1946).