Typical representatives of the nekton is the herring. It is well known that this fish has great commercial value. Until comparatively recently, it was promyshlyali in such large quantities that its price was very low, despite excellent taste and nutritional quality. In recent years, due to the sharp increase of the fishing fleet and introduction of intensive methods of production occurred overfishing. The number of herring in the oceans have decreased dramatically.
If in the future the intensity of the herring fishery will increase or even remain at current levels in the coming years, this valuable food fish will become a Museum rarity. Reduction of stocks of herring and concerned consumers and fishermen, but the first sounded the alarm scientists.
The appearance of the herring is well known to everyone, but it is unlikely that the layman can easily distinguish one kind of herring from another: the difference between them for the untrained eye to be insignificant. Species differences are not only in the details of the structure and the size of the fish, much deeper than they differ from each other in biology, numbers, distribution. Therefore, the fishery for mackerel fishes should be strictly subordinated to scientific data, to each type needs special approach.
The matter is complicated by the fact that herring form a set of subspecies. One subspecies can be mass, the other rare. One spawns in April, another in June. And the food composition of the different subspecies is different, and sexual maturity is reached at different years of life, and nutritional value varies, and externally, the fish are almost indistinguishable. Here they foraged all in a row.
Ocean herring are presented in the seas of the Russian Federation five subspecies, which differ in number of vertebrae, number of scales between ventral and podostemum fins, long pectoral fins, shape of head, teeth development, etc. to determine the subspecies status of fish, since it is pre-x-ray.
The collection of herring for the collection and subsequent storage requires especial caution: scales easily disappears, and without it, the fish loses its scientific value, since it is the number of scales judged on what subspecies of fish is one. Sometimes to pinpoint the systematic position of the herring, you have to consider and the number of Gill rakers.
While it was only about structure. But the different subspecies of herring and biology, and growth, and commercial value. Within the different subspecies of geographical races. The Atlantic herring such races as much as 7. In the white sea subspecies of the matter is even more complicated. There can be distinguished two forms: large with the two races and small — with three. In Kandalaksha and Dvina bays and meet large and small form in Onega.
The introduction of new methods of research have allowed to Refine the knowledge of its biology. The staff of the Zoological Institute of the tagged 38 780 white sea herrings. Then some of them were caught again. The result was to set the path and timing of movement of individual herds. It became very clear that in each Bay of the White sea are holding their own, the so-called local and isolated reproductive herd fish.
Analysis of the chromosome revealed significant differences between fish individual herds. So, within the Kandalaksha Bay of the large forms have 54 chromosomes, and small — 52. These studies provide the basis for development of rational fishing and artificial breeding of the herring.
Why should such artificial breeding? It turns out that in the conditions of the White sea herring ROE at 30— 100 per cent may die from desiccation during low tide (herring spawn in the intertidal zone). If the hatching for whatever reason, does not coincide with the emergence of their main food of juveniles of the crayfish Calanus, the larvae die from starvation. To prevent loss of eggs and larvae developed the technique of in vitro fertilization and subsequent transfer of eggs into the sea.
Plunging the eggs into the deeper colder layers, it is possible to delay the hatching of larvae to term. The combination of these activities at commercial hatcheries will allow you to save spawn and to protect juvenile herring in the early, most vulnerable stages of development.