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Herbivorous fishes: experience of acclimation.
Food shortages are the question of the day for a significant part of humanity, especially where animal products are concerned. On one hand, this situation is caused by the ever growing population numbers (world population topped 6.5 million early in 2006) and by the relatively low efficiency in the use of natural biological resources, on the other. For instance, only a ninth part of the world's dry land (13.6 bln hectares, or about 34 bln acres) has been put to use for agricultural purposes as cultivated fields. Hydrobionts (i.e. aquatic organisms) offer a good chance of raising the available food reserves. Today the overall annual fish catches in the World Ocean plus the fish grown in artificial lakes are above 145 mln tons, or over halfas much as the total output of meat. But while, according to informed expert opinion, the fish catch in the world's seas and oceans has already reached an annual maximum of 90 to 95 mln tons, aquiculture still has a substantial growth potential. Fish farming in man-made lakes and ponds is developing space: at the close of the past 20th century every fourth consumed fish was grown there. Over half of the world's aquaculture produce comes from freshwater continental lakes, and their potential is far from being exhausted.
The coordinated management of two ecosystems-water catchment areas and bodies of water proper-boosts significantly the productivity of lakes, ponds and other water pools compared with that of seas and oceans. Unlike dry land ecosystems their water analogs are characterized by certain distinctive features exerting a positive effect in activating the ongoing biological and energy-related processes. Autotrophs in the form of phytoplankton and macrophytes (e. g. algae) are distinguished by higher metabolism and productivity than land plants are. In water small particles combine into what we call "detrital shower"; such particulates are such particulates are decomposed and consumed much faster than in dryland systems. Pasture type food chains are characteristic of water bodies due to the great diversity of their animal and plant kingdom; the anatomy and physiology of the aquatic fauna is well adapted to the consumption of organisms of most different trophic levels. All the links ofthe food chain have fish species capable of consuming phytoplankton or zooplankton or benthos or fish or detritus. There are also piscine forms that consume organisms of different trophic levels (phytoplankton+zooplankton, zooplankton+benthos, phytoplankton+detritus, and so forth.)
Every body of water has a specific food chain of its own on which its productivity depends. Such ecosystems can be turned into high-performance structures either by bringing the economically valuable consumers closer to the primary links of the food chain or by supplanting the extant phytoplanktonphages by more productive and valuable species. At this point it will be in place to recall what Georgi Nikolsky (1910-1977), our foremost ichthyologist and corresponding member of the USSR Academy of Sciences, has said to this effect: "If we could succeed in getting the final, economically valuable bioproducts closer to producers i. e. obtain a maximum of bioproducts at least from the second chain of food chains, we would certainly be able to achieve a significant increase in the productivity of water bodies."
The total area of Russia's piscine lakes, ponds and other pools is about 30 mln hectares (75 mln acres). Their potential productivity is vast indeed. But given the present state of the aboriginal ichthyofauna, this natural wealth can hardly be put to good use since the primary links of the food chain are outside the economic turnover. Lacustrine ecosystems that took body and form over many centuries and that are characterized by a certain degree of homeostasis are poorly amenable to regulation because of their great complexity. Therefore it will be more expedient to remodel the ichthyofauna of lakes and ponds. Even so, this is no easy problem. First, the species-specific composition of fish in such bodies of water comprises piscine forms that formerly inhabited rivers and streams where conditions are essentially different from those in lakes and ponds, that is bodies of still water. Second, the fluvial ecosystem is remarkable for scant phytoplankton and abundant rheophilic species (those adapted to fast-flowing waters) and for the actual absence of phytoplankton phages. Consequently, we are focusing on high-productivity ecosystems developed on the basis of the available artificial bodies of water and their proper management. By coping with this problem we shall be able to pass from conventional fishing to fish farming by means of pasture-oriented aquaculture.
It is all-important in this context to select an ichthocomplex where herbivorous fishes, or consumers of the first order, would outnumber other forms and whose cultivation could yield a high economic return at minimeal expenses.
Exploring piscine communities in Eurasia's bodies of water we found there were several fish species in China feeding on phytoplankton, macrophytes, zooplankton and detritus. These forms exhibited high growth rates and fertility, and fairly rapid pubescence at that. This is why we chose several fish species of the Far East for resettlement in East European lakes and ponds, namely the silver carp (Hypophthalmichthys molitrix Val.); the grass (white) carp (Ctenopharyngodon idella Val.); the mottled carp (Aristichthys nobilis Rich.); and the black carp (Mylopharyngodon piceus Rich.). What are their concrete characteristics?
The silver carp subsists largely on phytoplankton and detritus, and does not enter into direct food competition with other species. Its joint cultivation with the common, or mirror carp (Cyprinus carpio) has a positive effect on both in terms of better growth and higher productivity.
The grass (white) carp is a selective herbivore. Under natural conditions it feeds mainly on zooplankton, or else on phytoplankton or detritus. Its overly dense embedment (population density per unit of area) can get it to compete with the common carp for zooplankton and inhibit the growth of both.
The mottled carp lives on higher aquatic plants. In ponds it performs as a biological ameliorator (scavenger), and controls algal growth in natural lakes.
The black carp is a biological scavenger consuming mollusks, which are the intermediate hosts of certain parasites; this way it improves the epizootic situation in ponds. Its cultivation is also good for water cooler ponds of thermal and nuclear power stations, where proliferation of mollusks interferes with the work of generators.
Incidentally, a hundred years ago Russia's ichthyologygists insisted on replenishing the fish population of European Russia with phytophages of the Far East. But this idea could not be implemented for lack of adequate knowledge about their biology and sexuality, and also because of the great distances to their natural habitats. According to foreign ichthyologists, grass and silver carps inhabiting rivers of monsoon climate did not grow hard and soft roe if transferred to still, stagnant bodies of water due to the specific characteristics of their native ecology. The fish scientists certainly had a point. Many abortive attempts made in different countries at acclimating herbivorous fish outside natural habitats readformed the opinion about the futility of the whole thing. The principal problem-that of obtaining progeny in ponds-could not be solved either at the time. One
could cope with it at a later date by drawing upon progressive methods of embryology, cytology, histology and other sciences. Proceeding accordingly, ichthyologists designed biological methods of acclimation, wholesale reproduction and breeding conditions for the "new settales" from the Far East.
Compared with the common carp, herbivorous fish are more heat-loving. The sum total of productive temperatures (above 15° C) ensuring the normal performance of the sex system should top 2600 degree/days. Therefore in Russia and CIS countries the boundary of steady reproduction for such fish is south of the 50th parallel. The North Caucasus, southern Ukraine, Moldova, Central Asia and Transcaucasia offer more favorable climatic conditions for spawning and hatching. Annual fluctuations of water temperature affect the rate and course of spawning. While along the northern boundary of the natural habitat (the Amur) females spawn intermittently (by stages), they do it but once in the North Caucasus, and several times a year in the tropics.
Nature grass and silver carp spawners inhabiting still waters yield good hard and soft roe with the use of an upgraded method of hypophysial injections. The technique works like this: upon the injection of hypophysial suspension the fish can spawn regardless of the natural spawning situation. Among the essential conditions needed for maturation are these: an adequate oxygen regime and water temperature not below 18 to 19° C. We practice piecemeal (double) injections so as not to upset the sequence of preparatory preovulatory processes and ovulation proper, as is the case with single, one-time injections. The first, preliminary injection activates the polarization of sex cell nuclei as a step to meiosis (meiotic, or reducing division), while the other, resolving one, stimulates ovulation.
In structure the roe of herbivorous fish differs much from that of the common, mirror carp. Their roe is spawned deep in the water and, upon fertilization, grows significantly in size. Water temperature should be 18 to 30° C, and oxygen concentration, not below 4 mg/l. Special hatcheries have been built in the All-Russia Institute of the Freshwater Fish Industry (at Rybnoe in the Dmitrov District ofthe Moscow Region) for roe and fry incubation. The technology of silver and grass carpbreeding takes in an extra growth-promoting stage, which boosts the survival rate of small fry.
The introduction of first-order consumers to the ecosystem of conventional carp-raising ponds-intensively exploited as they are - made it possible to obtain a significant amount of additional produce. The food chains were shortened, and the feeds not consumed by the common carp became a basic diet for grass and silver carps. Fish farms in the country's south grow at least 800-1000 kg/ha of marketable produce without an extra expenditure of fodder and fertilizer-all that thanks to the innovative technology.
The natural productivity of pond fishing areas can be increased in a variety of ways: by building up the mass of matter drawn into the biological turnover; by speeding up the turnover rate; by enhancing the efficiency of organic matter utilization and energy accumulation within the bounds of trophic levels; and by truncating the food chains. A considerable part of these processes is regulated via modification of the qualitative composition and trophic structure of biological communities in a pond; this is largely achieved by introducing herbivorous fish into the ecosystem. Such herbivores are playing a special role in large bodies of water over 10,000 ha (25,000 acres), in cooler water reservoirs of power-generating facilities with a definite temperature regime, and in small lakes of irrigation systems or inpotable water pools.
Such fish species are likewise much effective in all-purpose water pools under 1000 ha (25.000 acres). Young grass and silver carps can reconfigure respective ecosystems by filling in the empty food niche of phyto-planktonphages or by eliminating the profuse overgrowth of higher aquatic plants or by supplanting the extant aboriginal piscine species, all the more so that the "new settlers" are superior in productivity. As shown by a large-scale experiment carried out in small irrigation pools of the North Caucasus, their productivity was up to 800 kg/ha after herbivorous fish-the silver carp predominantly-had been brought there. Expanding the fish population to 8 species in water bodies of the Astrakhan Region (silver and mottled carps, grass and black carps, three buffalo fish species, common carp), it became possible to double the output! Good results are on record after silver and black carps had been let into the Tsimlyansk artificial lake, where as much as 2 thousand tons of herbivorous fish is caught every year, with individual specimens weighing 10 to 15 kg. Such fish species likewise increased the productivity of cooler ponds at many thermal and nuclear power stations.
Herbivorous fish can play a very important role in consuming the feed resources of major water pools wherever there are free food niches, especially in the primary links of the trophic chain. This is particularly true of phytoplankton and macrophytes the species-specific and quantitative presence of which is restricted in fluvial ecosystems. The hydrological regime of water reservoirs (water circulation, concentrations of foreign organic substances) stimulates the profuse growth of microalgae and the resulting water-bloom, which brings down the quality and productive potential of the aquatic medium. As a phytophage the silver carp can improve the ecosystem at the expense of algal bloom.
The abundant growth of higher water plants in fish-raising ponds leads to an excessive accumulation of organic wastes and bogging; it impairs the hydrochemical regime and contracts fishing areas. Macrophytes generate problems for cooler ponds of thermal power stations, too, by problems impeding the circulation of water streams and causing backwater; all that reduces considerably the cooling capacity of ponds. In irrigation systems macrophytes slow down the flow rate several-fold and thus cut dramatically the throughput capacity of canals and ditches. It is best to combat algal proliferation by biological methods, specifically, by introducing commercially valuable fish species, the grass carp in particular. It conforms to all standards of scavenger fishes: a wide food spectrum; vigorous consumption of plants: trophic elasticity: tolerance for oxygen growth deficiency; fast growth; and high commodity and taste qualities. By regulating the population of predators and easing their pressure in the predatorphytophage-algae chain, phytophages can attain to a large population and biomass, and thus reduce the amount of primary producers and keep algal growth under control.
And last, the bringing of herbivorous fish into established ecosystems is no cause for worry: there will be no danger of their rampant proliferation, for the absolute majority of water pools lack proper conditions for an natural spawning of silver and grass carps. Consequently, their species diversity and population are controlled by man who will be introducing herbivores depending on the available feed stock and presence of predators. The economic effect of their resettlement into large bodies of water is determined above all by the number of young fish per unit of area. The experience of the use of natureal resources in the Tsimlyansk, Veselovsky, Proletarsk and other large reservoirs in Russia's south has demonstrated the real possibilities of achieving annual catches of several thousand tons of silver carps, each weighing over 10 kg, with high consumer qualities. The thirty-year life of herbivorous fishes in these man-made lakes has not impacted the species-specific and quantitative mix of the aboriginal ichthyofauna. Summing up, we might as well say: in the last quarter 20th century the productivety of fish-breeding ponds went up 3 to 5 fold country wide thanks to the full-scale introduction of silver and grass carps, and their share in the total output of marketable fish is close to 40 percent today.
The acclimation of herbivorous fishes in Russia's lakes and ponds is a spectacular example of the scientific-technical revolution in the domestic fish industry.
Dr Alexei Bagrov, Andrei Bogeruk and Coworkers were awarded a prize of the Government of the Russian Federation (2005) for working out the scientifically substantiated new methods of boosting the efficiency in using the natural production potential, biological amelioration and building up strategic food reserves in Russia's inland water pools and for industrial assimilation of these innovative methods.
Травоядные рыбы: опыт акклиматизации.
Нехватка продовольствия - это вопрос дня для значительной части человечества, особенно в том, что касается продуктов животного происхождения. С одной стороны, такая ситуация вызвана постоянно растущей численностью населения (в начале 2006 года численность мирового населения превысила 6,5 миллионов человек), а с другой - относительно низкой эффективностью использования природных биологических ресурсов. Например, только девятая часть засушливых земель в мире (13,6 миллиарда гектаров, или около 34 миллиардов акров) была использована в сельскохозяйственных целях в качестве обрабатываемых полей. Гидробионты (т.е. водные организмы) дают хорошие шансы увеличить имеющиеся запасы пищи. Сегодня общий годовой вылов рыбы в Мировом океане плюс рыба, выращиваемая в искусственных озерах, превышает 145 миллионов тонн, или более половины общего объема производства мяса. Но хотя, согласно обоснованному мнению экспертов, вылов рыбы в мировых морях и океанах уже достиг годового максимума в 90-95 миллионов тонн, аквакультура по-прежнему обладает значительным потенциалом роста. Рыбоводство в искусственных озерах и прудах - это развивающееся пространство: в конце прошлого 20-го века там выращивалась каждая четвертая потребляемая рыба. Более половины мировой продукции аквакультуры поступает из пресноводных континентальных озер, и их потенциал далеко не исчерпан.
Скоординированное управление двумя экосистемами - водосборными площадями и собственно водными объектами - значительно повышает продуктивность озер, прудов и других водных бассейнов по сравнению с продуктивностью морей и океанов. В отличие от экосистем суши, их водные аналоги характеризуются определенными отличительными особенностями, оказывающими положительное влияние на активизацию текущих биологических и энергетических процессов. Автотрофы в виде фитопланктона и макрофитов (например, водорослей) отличаются более высоким метаболизмом и продуктивностью, чем наземные растения. В воде мелкие частицы объединяются в то, что мы называем "осколочным дождем"; такие частицы являются такие твердые частицы разлагаются и расходуются гораздо быстрее, чем в системах засушливых земель. Пищевые цепи пастбищного типа характерны для водных объектов из-за большого разнообразия их животного и растительного мира; анатомия и физиология водной фауны хорошо приспособлены к потреблению организмов самых разных трофических уровней. Во всех звеньях пищевой цепи есть виды рыб, способные потреблять фитопланктон, зоопланктон, бентос, рыбу или детрит. Существуют также формы рыб, которые потребляют организмы разных трофических уровней (фитопланктон + зоопланктон, зоопланктон + бентос, фитопланктон + детрит и так далее).
Каждый водоем имеет свою собственную специфическую пищевую цепочку, от которой зависит его продуктивность. Такие экосистемы могут быть превращены в высокопроизводительные структуры либо путем приближения экономически ценных потребителей к первичным звеньям пищевой цепи, либо путем вытеснения существующих фитопланктонфагов более продуктивными и ценными видами. Здесь уместно вспомнить, что сказал по этому поводу Георгий Никольский (1910-1977), наш выдающийся ихтиолог и член-корреспондент Академии наук СССР: "Если бы нам удалось приблизить конечные, экономически ценные биопродукты к производителям, то есть получить максимум используя биопродукты, по крайней мере, из второй цепочки пищевых цепочек, мы, безусловно, смогли бы добиться значительного увеличения продуктивности водных объектов".
Общая площадь российских рыбных озер, прудов и других бассейнов составляет около 30 миллионов гектаров (75 миллионов акров). Их потенциальная производительность действительно огромна. Но, учитывая нынешнее состояние аборигенной ихтиофауны, это природное богатство вряд ли может быть использовано с пользой, поскольку первичные звенья пищевой цепи находятся вне экономического оборота. Озерные экосистемы, которые формировались на протяжении многих столетий и которые характеризуются определенной степенью гомеостаза, плохо поддаются регулированию из-за их большой сложности. Поэтому целесообразнее будет реконструировать ихтиофауну озер и прудов. Тем не менее, это непростая проблема. Во-первых, видоспецифический состав рыб в таких водоемах включает рыбообразные формы, которые ранее обитали в реках и ручьях, где условия существенно отличаются от условий в озерах и прудах, то есть водоемах со стоячей водой. Во-вторых, речная экосистема примечательна скудным фитопланктоном и обилием реофильных видов (приспособленных к быстротекущим водам), а также фактическим отсутствием фитопланктонных фагов. Следовательно, мы фокусируемся на высокопродуктивных экосистемах, созданных на основе имеющихся искусственных водоемов и надлежащего управления ими.
