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Скачать бесплатно! Научная работа на тему BESTER FISH: FARING WELL?. Аудитория: ученые, педагоги, деятели науки, работники образования, студенты (18-50). Minsk, Belarus. Research paper. Agreement.

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By Igor BURTSEV, Cand. Sc. (Biol.), leading researcher at the federal amalgamated enterprise "All-Russia Research Institute of Fishing and Oceanography"; Alexander NIKOLAYEV, department head at the same research institute

Sturgeon fish are a dainty to grace any table. Not to speak of their soft and pressed caviar. But under natural conditions their growth period is quite long, from 10 to 15 years and even more (and it is 25 years for the beluga, or white sturgeon). These fish fall victim to open-ended poaching and man-caused effects on water systems. Hence the disastrous shrinking of their population. There are two ways of reversing the downtrend: better stewardship of fish resources and breeding new varieties of noble fish that could grow within a limited space (lakes, fish-ponds, stews). Now let us look into the latter most promising option.

Way back in the 1850s Vladimir Vrassky, the founder of Russia's first fish-factory, suggested breeding the sterlet in fish-ponds. In fact, the very idea of fish-farming came from him. And the first successful experiment on artificial insemination of sterlet roe with the milt of regular sturgeon and stellate (starred) sturgeon was carried out in 1869 by Academician Fyodor Ovsyannikov who predicted a great commercial future for the hybrids thus obtained. As decades later, in the 20th century, many rivers came to be dammed (and such dams closed the natural passages for spawning sturgeon), one pondered: why not breed varieties that could fare fine in ponds or lakes, not only in rivers and streams?

The intensive construction of hydraulic systems in the 1950s, which gave rise to a string of man-made lakes (on the Volga and the Dnieper in particular) spurred fish-

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related studies. Dr. Nikolai Stro-ganov's monograph published in 1969 provides essential data on growing the sturgeon fish in ponds and lakes, and on their acclimation under new conditions.

Now what concerns the sturgeon fish. Another biologist, Dr. Nikolai Nikolyukin, began his experiments on sturgeon fish hybridization in 1949, that is at about the same time as Dr. Stroganov did. For as long as 29 years Dr. Nikolyukin kept experimenting with the sturgeon, sterlet, beluga and stellate sturgeon. Among other things, he tried what we call reciprocal crossings* of the beluga (white sturgeon, Huso huso) with the sterlet (Acipenser ruthenus); however, the results of such attempts were absolutely unpredictable because of the taxonomic remoteness of these species (that is their possible incompatibility) and their striking differences.

Surprisingly, the thus obtained hybrid, foredoomed as it seemed, proved a phenomenal success, commercial success too. Dubbed "bester", it propagated fast, and became an object of further studies. The biotechnology of breeding sturgeon fish in closed fresh- and sea-water bodies of water received particular attention. Spawning schools, the breeders, were a special concern.

Experimental breeding of the bester and other hybrids continued for over ten years in the ponds of a fish-farm at Saratov and, as of 1963, at Rostov. It turned out that the bester, growing to 1.5 m in length (something it has inherited from the beluga fish, for sterlets are never longer than 60 cm), is in need of extra feed, for the amount of natural feed a valuable in ponds is not enough. According to one of the authors of the present article, Igor Burtsev, the intensive feeding offish of little value to sturgeon hybrids stimulates their rapid growth, and activates their gametogenesis* and pubescence.

There were also attempts at growing besters in large open bodies of water. In 1962 to 1969 Dr. Nikolyukin experimented with hybrid fry let out into a large brackish reservoir at Rostov and into the Gulf of Taganrog (Azov Sea). The results beat all expectations. Young fishes gained a mass of 400-500 g in their first year, two-year- olds grew to 1.5-2 kg, and five-year-olds-to as much as 12 kg, or far more than did fishes reared in fresh-water lakes and ponds.

It seemed all right. And yet... There came two threats. First, from poachers virtually wiping out the bester population. Second, from the possible genetic contamination of pure sturgeon species, the white sturgeon (beluga) above all. Considering all that, the breeding of valuable fish varieties had to be confined to farms of intensive aquicul- ture*. Besters of the first generation only were used for many years, their fry supplied by specialized fish-factories. The commercial output of these noble fishes soared to 150-200 tons a year, something unprecedented in world practice.

It usually takes 10 to 15 generations for new fish species to form in

* Gametogenesis- growth of sex cells (gametes) in females (oogenesis) and in males (spermatogenesis).- Ed.

* Reciprocal crossings-two crossings when each of the genetically different parental forms is used first as a maternal and then as a paternal one.- Ed.

** Aquiculture-breeding of aquatic organisms (fishes, mollusks, crayfish, lobsters, algae) under controlled conditions. -Ed .

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full. This is why it was important to trace changes, if any, in the bester's second, third and subsequent generations. This work was carried out by the All-Union (now All- Russia) Institute of Fishing and Oceanography under the guidance of Dr. Nikolai Nikolyukin and Dr. Lada Dushkina. Taking part in the research team were Drs. Yelena Serebryakova and Viktor Arefiev. This is what the case study showed: a cytogenetic imbalance (disturbance or mismatch of chromosomal complexes) could be observed in the second generation of hybrid fish. As a result, cell division in many of the roes (up to 20 percent) took an "erratic" course, and the embryos died. To avoid such mishaps the team resorted to family selection for the bester's further reproduction and chose the best breeders proceeding from the earlier time of pubescence. The pedigree groups thus formed did not miscarry in cytological terms and produced viable progeny. The third selectional generation exhibited appreciable stabilization of the quantitative characteristics of kary-otypes (totality of chromosomes); thus genetic homeostasis (species stability) was restored to some extent.

Besides the main reciprocally crossed forms of bester (beluga crossed with the sterlet and vice versa) that got equal shares of heredity from the initial species, our biologists obtained what is known as backcrosses, i.e. a hybrid crossed with parental species (bester crossed with beluga or sterlet). Its hereditary characteristics is three-quarters of the beluga's or sterlet's makeup, respectively, which means that the new hybrids became similar in their characteristics to the ancestral species. This work, which was started in the 1960s and 1970s at a fishing farm near Rostov in Russia's south, is still being carried on by Kazachka, a commercial enterprise.

Our senior researcher Dr. Vera Krylova has made a thorough study of the morphology of different forms and generations of hybrid fish. Says she: All of them differ in certain meristic (somatic) and plastic (oral) characters.

Our research center suggested three hybrid besters as the most promising ones in commercial terms, and these are: Burtsevskaya that has 50 percent of the blood (percentage of genotypes) of both beluga and sterlet; Vnirovskaya, with 75 percent and 25 percent respectively; and Aksaiskaya, with 25 percent and 75 percent. The government committee in charge of selection work approved our suggestions in 2000. Here are some of the

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data: mature females and males of the Aksaiskaya variety build up a mass of 3 and 2 kg respectively; those of the Burtsevskaya variety- 8 kg and 4 kg, and those of the Vnirovskaya, 30 kg and 12 kg. Another consumer index: the output of commercial fish per million of fertilized roes: for the Burtsevskaya variety it is 176.4 tons; as much as 122.5 tons for Vnirovskaya, and 94.0 tons for Aksaiskaya.

In a nutshell, the bester hybrid lived up to our expectations: our research scientists ventured out into a risky experiment that might entail unpredictable consequences- they crossed the beluga and sterlet fish, the species poles apart ecologically, morphologically and biologically. It took a few decades to effect initial crossings, make all-out studies of the hybrids in three generations, of their homeostasis and fertility, embryogenesis (embryonic growth), and of their morphological, physiological and biochemical characteristics. The bester hybrid can now be monitored both in its cytogenetic characters and in its marker protein genes whereby fish species can be told apart. Work is afoot to upgrade the monitoring techniques as to the quality of offspring, viability, and growth rates.

Aside from Russia, besters are also cultivated in Poland, Germany, Hungary, Italy, Japan, the United States and in other countries. We plan to certify a new generation of spawning schools according to phenotypic* characters. In addition to that, we should select breeder mates that could match their genotypes with the utmost efficiency. A search for new methods of selection and rational feed is another line of our work.

* With reference to phenotype, or totality of all the characters and properties of the organism that have been formed in the process of its development.- Ed.


Опубликовано 10 сентября 2018 года

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