Introduction

Sturgeon, fish of extremely great commercial value, belong to one of the most ancient groups of the Osteichthyes. They are widely distributed in the Northern Hemisphere above the 30th parallel, and within this zone they are found everywhere along the coasts of the Atlantic and Pacific Oceans, the Medi­terranean and Black seas, as well as in rivers, lakes and inland seas. Their abundance in this huge range differs greatly: in many parts of the range they are found only as isolated, sparse populations and occur in significant numbers only in a few regions. The highest concentration of sturgeon is in the seas of the Ponto-Caspian depression, -the Caspian, Azov and Black seas. The Caspian represents a unique reservoir: in recent years it has produced up to 92% of the sturgeon catch in the USSR (Barannikova 1987).

The sharp fall in the abundance of sturgeon in many regions, and their complete disappearance in some places has been taken by many researchers as an indication that they are a relic group of fish doomed to extinction as a result of competition with higher fish (cf. Magnin 1959; Gerbil'skii 1962). Although the Acipenseridae indeed are an ancient group of the Osteichthyes, they are beautifully adapted to contemporary environmental conditions and even have great advantages as compared with the Teleostei. These advantages include: wide range of spawning temperatures, longer retention of fertilizability by sperm and eggs in water, early euryhalinity of juvenile fish and the broad spectrum of their feeding, prot-ection from predators afforded juvenile fish by their scutes, ecological plasticity as expressed in the existence of anadromous, semianadro­mous and freshwater forms, etc. The decrease in the abundance of sturgeon throughout the world isa result of human activity: fishing over thousands of years, and, at present, the regulation of the flow of rivers and their pollution, and mass destruction of juvenile sturgeon as a result of their being incidentally caught in small-mesh nets intended for teleost fish, and other factors (Gerbil'skii 1962; Marti 1964). Therefore, the problem of conserving sturgeon and replenishing their stocks in the entire range has become urgent for scientists of various countries. The authors of this book hope that the materials given here will prove useful in solving this difficult but important problem.

The family of sturgeon, Acipenseridae, includes four genera containing 24 species; 17 of them belong to the genus Acipenser (sturgeon), two to the genus Huso (giant sturgeon), two to the genus Scaphirhynchus (shovel-nosed sturgeon) and three to the genus Pseudoscaphirhynchus (Aral shovelnoses). Thirteen species reside in USSR territory (Berg 1948). These are the two species of the

T. A. Dettlaff et al., Sturgeon Fishes© Springer-Verlag Berlin Heidelberg 1993

2 Introduction

genus Huso: H. dauricus (Georgi) (kaluga, giant Siberian sturgeon) in the Amur basin and the Amur estuary and H. huso (L.) (beluga, giant sturgeon) in the Caspian and Black seas from whence they migrate into the rivers. The genus Acipenser includes: A. gueldenstaedti Brandt (Russian sturgeon) living in the Caspian from whence they migrate into rivers to spawn, and its subspecies, A. g. colchicus V. Marti (Black-Azov-sea sturgeon), as well as A. persicus Borodin (Persian sturgeon) in the Caspian Sea. There are also A. baeri Brandt (Siberian sturgeon) in the rivers of Siberia, beginning with the Ob' and extending to Kolyma, and its subspecies, A. baeri chatys Drijagin (little Siberian sturgeon) living in the Lena and Kolyma basins; A. schrencki Brandt (Amur sturgeon) in the Amur basin; A sturio L. (Baltic sturgeon) in the Baltic and Black seas and their basins; A. medirostris Ayres (Sakhalin sturgeon in Asia or green sturgeon in north America) in the seas of Japan and Okhotsk. To the same genus belong also A. stellatus Pallas (sevryuga, stellate sturgeon) inhabiting the Caspian, Azov and Black Seas and their basins; A nudiventris Lovetzky (bastard sturgeon) in the Black, Caspian and Aral Seas and their basins; A. ruthenus (L.) (sterlet) in the rivers of the Black and Caspian Sea basins, in the basins of lakes Ladoga and Onega, in the Severnaya Dvina, Ob' and Enisei. There are also three species belonging to the genus Pseudoscaphirhynchus, which inhabit the Aral sea basin: P. kaufmanni (Bogdanow) (big Amu Darja shovelnose) as well as the rare P. hermanni (Kessler) (little Amu Darja shovelnose) and P. fedtschenkoi (Kessler) (Syr-Darja shovelnose).

The majority of sturgeon species are not abundant outside the USSR. According to data presented by the French ichthyologist Magnin (1959), sturgeon had practically disappeared in the Mediterranean and Adriatic by the middle of the 20th century and only rare individuals of A. sturio, A. naccarii Bonoparte and H. huso are found. Only A. sturio are found on the Atlantic coast of Europe. H. huso, A. gueldenstaedti colchicus, A. stellatus, and A. nudiventris migrate from the Black sea into the Danube. A. ruthenus also occurs in the Danube. H. huso, A. persicus, A. stellatus, and A. nudiventris which are found in the southern part of the Caspian spawn in rivers of the southern coast.

In America there are five species of the genus Acipenser: on the Pacific coast, A. medirostris and A. transmontanus Richardson (white sturgeon); on the Atlantic, A. oxyrhynchus Mitchill (Atlantic sturgeon), A. brevirostrum Lesuer (short-nosed sturgeon) and, in fresh waters, A. fulvescens Rafinesque (lake sturgeon), as well as two species of the genus Scaphirhynchus: S. platorhynchus (Rafinesque) (shovel-nosed sturgeon) and S. albus (Forbes et Richardson) (pallid sturgeon).

Finally, five species of sturgeon occur on the Asian coast of the Pacific: A. medirostris; in China, rarely A. sinensis Gray (Chinese sturgeon) and A. dabry­anus Dumeril (Korean sturgeon), and, in Japan, still more rarely, A. micadoi Hilgendorf and A. kikuchii Jordan et Snyder.

A large part of the entire world catch of sturgeon (about 90%) is in the USSR (Barannikova 1987). Of greatest commercial importance are: A. gueldenstaedti

Introduction 3

and A. gueldenstaedti colchicus, A. stellatus, and H. huso. Catches include also A. baeri, A. nudiventris, H. dauricus, and A. ruthenus.

Outside the USSR the largest catch belongs to Iran (in the southern Caspian). In Europe sturgeon (in small quantities) are caught in Rumania, Bulgaria and Portugal. In the USA there is fishing for A. sturio, A. medirostris, A. trans­montanus, and A. fulvescens, as well as S. platorhynchus and S. albus.

Sturgeon include anadromous species (living in the sea and migrating into rivers to spawn), semianadromous species (which spend most of their lifetime in rivers and make migrations into pro-estuarine regions, but do not go out into the open sea), and river-resident (freshwater) species which spend their entire lifetime in rivers. Some species, as for example A. baeri and A. ruthenus, have both semianadromous and river-resident forms.

At the present time, in the USSR the flow of most rivers in which sturgeon used to spawn has been regulated. This deprived sturgeon of the major part of their natural spawning grounds. In view of this, great attention is given to artificial propagation in order to preserve the diversity of sturgeon species and maintain their numbers. Since the decrease in abundance of sturgeon is not due to insufficient adaptation or competitive relationships with teleosteans, replen­ishment of their stocks by means of hatchery propagation of various sturgeon species seems quite practical.

The first experiment of artificial propagation of sturgeon was carried out in 1869 when Owsjannikow (1871) artificially inseminated A. ruth en us eggs, incu­bated them, and obtained prelarvae. In subsequent years, insemination and incubation were also performed for some other sturgeon species: A.fulvescens by Seth Green in 1875, A. sturio by Frauen in 1881, A. stellatus in 1884 and A. gueldenstaedti in 1899 by Borodin (Borovik 1916). These and similar experi­ments were aimed mainly at obtaining materials for investigation. The first experiment specially for fish culture was carried out in 1886 by Mohr who released 500000 A. sturio larvae in the Elbe. However, despite the relatively successful results of the first experiments, most of the work on artificial propagation remained small-scale for a long time. This was mainly due to difficulties in obtaining mature spawners which were caught on spawning grounds.

Derzhavin was the first to stimulate maturation of sturgeons (Derzhavin 1938, 1939, 1947). He placed them in conditions close to those found in nature during the migration to spawning grounds: they were kept in a basin with strong circular flow and pebbly bottom. In these conditions a few females matured, but this could not ensure the mass propagation of sturgeon.

The scientific principles of hatchery propagation of sturgeon were laid down by long-term investigations of Nikolai L. Gerbil'skii and his coworkers. They developed a method of pituitary injections for stimulating maturation of sturgeon (Gerbil'skii 1941, 1947). This method allows the obtaining of large amounts of eggs suitable for fish breeding from females caught in prespawning condition. Such a method is indispensable for hatchery propagation of sturgeon.

4 Introduction

Contemporary sturgeon culture in the USSR widely uses hatchery reproduction and refined biotechnology.

Work on artificial propagation of sturgeon has recently been started in many countries: USA, France, Italy, Hungary, Poland, China, Japan, etc. In the USA successful attempts to reproduce A. transmontanus, A. oxyrhynchus, and A. brevirostrum have been made. A major advance has been made with A. transmontanus (Doroshov et al. 1983).

However, a marked difficulty has arisen recently in obtaining suitable brood stock for fish culture: the number of females not responding to gonadotropic hypophysial hormones by reaching maturity has sharply increased. As a result of flow regulation in rivers and change in their hydrological regime, the migratory behavior of sturgeon, dynamics of their movements and the structure of their populations have changed, as well as the physiological condition of spawners (Barannikova 1979). At the present time, sturgeon fishery managers are faced with new problems, which a wide circle of scientists and practical fish culturists are trying to solve. These problems include the development of fish hatchery methods for various species and populations, development of methods for in vivo evaluation of gonad maturity, and selection of brood stock, as well as for eliminating losses of eggs, embryos, prelarvae, larvae and juveniles. The problem of water is critical, since pollution of water by oil and inadequately purified sewage water causes the condition of spawners to deteriorate and periodically produces mass extinction of prelarvae at the hatcheries. Also, the preservation of natural spawning, the improvement of existing and creation of artificial spawning grounds are very important tasks.

The efficiency of hatchery propagation is a well established fact: individuals of H. huso migrating from the Caspian into the Volga and Ural belong to those generations when natural spawning grounds have already been lost, i.e., they were raised at the hatcheries. At the same time a sharp increase in the abundance of H. huso juveniles has been noted in the northern Caspian. Stocks of sturgeon in the Azov sea are also mainly due to hatchery reproduction, since natural spawning in the Don is almost non-existent.

At present, there are 26 sturgeon hatcheries in the USSR (Barannikova 1987), most of which are located in river estuaries or nearby dams: in the Caspian sea basin - eight on the Volga, three on the Kura, one on the Terek, and one on the Sulak; in the Azov sea basin - three on the Don and four on the Kuban': in the Black sea basin - one on the Dniepr and one on the Rion; in Siberia - four hatcheries. Sturgeon hatcheries release annually 100-140 million juveniles in natural water bodies. In all, since 1975 more than a billion juveniles of H. huso, A. gueldenstaedti, A. stellatus, and A. nudiventris have been released.

Hatcheries provide for various stages in the biotechnological chain of fish culture: work with spawners, insemination and incubation of eggs, rearing of prelarvae, raising juvenile fish in ponds, keeping account of and distributing juvenile fish, and also the growing of live food. In many hatcheries three species of sturgeon are raised, in some, two. For keeping brood stock, hatcheries have isolation areas, and some hatcheries have temperature-controlled production

Introduction 5

lines designed by B. N. Kazanskii for long-term keeping of brood stock. These lines make it possible to keep fish until they complete stage IV of maturity (cf. Trusov 1964a), i.e., until they acquire the ability to respond to pituitary injection by maturation. Also, it is possible to keep them in such a condition at low temperature for two-three months and thus extend the period, during which they can be used for fish culture (Kazanskii 1963; Kazanskii and Molodtsov 1974).

The first information about embryology of sturgeon was given by Kowalew­sky et al. (1870) who described development of the embryos and prelarvae in A. ruthenus. These observations were later supplemented, mainly by Salensky (1878, 1880, 1881). Later embryological studies, which were carried predomin­antly on A. ruthenus, touched upon development of individual organs. However, studies of sturgeon development are of great scientific interest in comparative-embryological aspect. The Acipenseridae are an ancient group of fish that preserved primitive structural features relating them to the Chondrostei. At the same time, in the structure of eggs they are very similar to the Amphibia, since in the eggs of these groups, unlike most ofthe Teleostei, yolk inclusions are distributed over the cytoplasm. Hence, these groups are similar in many features of morphogenesis, in which the Acipenseridae differ from the Teleostei. Sturgeon can be used easily in developmental, physiological, and biochemical studies due to the high viability of embryos and possibility of obtaining large numbers of the embryos of the same age at the hatcheries. At present, sturgeon are similar to amphibians in the degree of our knowledge about their development. It will be seen later that many current problems of developmental biology are being studied using sturgeon embryos.

On the other hand, studies of sturgeon development are important for scientific improvement of fish culture methods. These studies include investiga­tions into mechanisms of hormonal regulation of the transition of fish from the prespawning condition to the spawning one, mechanisms of oocyte matura­tion, fertilization, development of embryos and prelarvae. Another subject is sources of losses and causes of various defects during embryonic and prelarval development.

The present book gives an account of the contemporary state of our knowledge of these questions with special emphasis on practical sturgeon­culture problems. The book summarizes results of many years of investigation by the authors and their coworkers at the D. P. Filatov Laboratory of Experimental Embryology of the N. K. Kol'tsov Institute of Developmental Biology, USSR Academy of Sciences. Also summarized are appropriate data from the literature.

Studies were carried out predominantly on A. gueldenstaedti, A. guelden­staedti colchicus, A. stellatus, and H. huso. In addition, the development of A. ruthenus and prelarval development of P. katifmanni were studied.

Structure of embryos of different Acipenserid species is very similar. There­fore, developmental stages can be characterized by a sum of features common for all studied species. We have identified 35 successive stages of embryonic

6 Introduction

development. They were first described for A. stellatus and illustrated with photographs of the embryos of this species and, for comparison, embryos of A. gueldenstaedti and H. huso at some stages (Dettlaff and Ginsburg 1954). These stages were later described for A. gueldenstaedti colchicus and illustrated with drawings given in this book. These illustrations have already been published, partly (Ginsburg and Dettlaff 1955, 1969) and in full (Ginsburg and Dettlaff 1975; Dettlaff et al. 1981).

In the development of sturgeon prelarvae ten stages were identified which are characterized by a complex of common features. However, during this period there are more species-specific differences increasing with the age of prelarvae. These stages were described previously for embryos of H. huso and illustrated with photographs (Schmalhausen 1968). In this book the development of prelarvae, as well as embryos, is described for A. gueldenstaedti colchicus in comparison with H. huso, A. stellatus, A. ruthenus, and P. kaufmanni. Drawings of successive stages of prelarval development include those previously published for A. gueldenstaedti colchicus (Schmalhausen 1975) and H. huso (Dettlaff et al. 1981) and unpublished drawings of consecutive stages in the development of P. kaufmanni.

The book is complete with eight appendices containing recommendations for practical use at sturgeon hatcheries. Temperature is given everywhere in degrees Celsius.

The authors collected the materials and carried out experiments annually, since 1949, at various fishery stations and sturgeon hatcheries: for many years on the Don (at the village Rogozhkino and the Rogozhkino sturgeon hatchery) and on the Volga (at the Volgograd and the Ikryanino sturgeon hatcheries and at the Saratov division of All-Union Scientific Institute of Maritime Fisheries and Oceanography, and, in separate years, - on the Kuban' (in Kadushkino and Temryuk), the Kama (in Rybnaya Sloboda) and on the Kura (in Mingechaur, at the Kura experimental and Ust'-Kura sturgeon hatcheries). Some of these stations (Kadushkino, Saratov, Mingechaur, Rybnaya Sloboda) and the Volgograd hatchery are located in the area of spawning grounds, while the others - in the lower river flow and in the delta areas. Investigations were carried out with the constant aid of workers at the Ministry of Fisheries and its divisions, and with the active assistance of fish culturists. The authors express their deep thanks to them all.