Sakhalin Sturgeon Аcipenser mikadoi (Hilgendorf, 1892): Searching for Technology of Artificial Propagation in Aquaculture

It shows searching for a solution to the issue of the stock rebuilding of the Red List species — the Sakhalin sturgeon. It describes the results of the expedition to the Tumnin river aimed at brood fish procurement and optimization of the technology for its reproduction together with the brood fish grown in aquaculture. It lists the morphological characteristics and fish-cultural and bio-data of the spawner caught in the Tumnin river and the milters grown at the Anyuy Sturgeon Fish Hatchery. A method for the obtainment of reproductive products, hatching and juvenile fish growning is described. As a result of sampling for biopsy, it has been found that the coefficient of oocytesʼ nucleus polarization was 7.4 on the average. The hormonal preparation surfagon was used for sex products stimulation at males and a female. The female ovulated in 12 hours after permitting injection. It was managed to get 2,378 g eggs on the average 87.6 per cent of fertilization. The average ejaculate volume was 455 ml. The spermatozoon mobility at mean 14 °C temperature made up 208 sec. A double fertilization method was used at fertilization of an eggs part, moreover the eggs received were of a high piscicultural quality (99%). The average diameter of swollen eggs was maximum 6.8 mm and minimum 6.6 mm after fertilization. The larvae production made up to 30%, i.e. 27,850 of incubated eggs. 1000 ongrown fry were stocked into the Tumnin river, the last juveniles were directed to fish cultural farms of Russia with a view to form there recruitment-and-brood stocks. According to results of experimental works, done in the Anyuy Fish Hatchery, the first provisional technology of work was recommended on fertilized eggs production from the Sakhalin sturgeon spawners after the schema “a wild female + farmed males” by a method of a double fertilization with the increased exposition time.

Development of a set of oligonucleotides for the identification of the Sakhalin sturgeon Acipenser mikadoi Hilgendorf, 1892 by PCR

Sturgeons (family Acipenseridae) are valuable commercial fish and aquaculture resources. The Acipenser genus includes about 20 species, 12 of which are recorded for the Russian territory. One of the rarest is the Sakhalin sturgeon A. mikadoi Hilgendorf, 1892. At present, its population size is significantly decreased and the species is close to extinction. Natural populations of the species have survived in the Tumnin River in Khabarovsk Region and the Viakhtu River in Sakhalin Region. Vihtu River in Sakhalin Region. Due to the small numbers of rare and endangered fish species, noninvasive approaches, including the use of DNA from the environment, appear to be the most suitable for monitoring their species and genetic diversity. The method is well established in this area and has been successfully tested for the monitoring of several species of rare and endangered sturgeons. This paper presents the results of the development of primers specific for the mitochondrial DNA of the species A. mikadoi. A matrix of 15 sequences of complete mitochondrial genomes from 3 sturgeon species whose ranges may overlap - A. mikadoi (KX276658), A. dauricus (KJ402277) and A. schrenckii (MH973728- MH973734, KX276660, KX276659, KF150287, KC905169, KC820796) - was generated. A. medirostris (NC_028405), which is genetically closest to the Sakhalin sturgeon, was also included in the analysis. A sliding window algorithm was applied to the sequence matrix. A graph showing the distribution of divergence values along the mitochondrial genome of sturgeon was plotted based on the results of the analysis Fig. 1. Based on matrices of individual genome fragments (16S rRNA, COI, ND1, and D-loop), a search for species-specific primers was performed in the DECIPHER program. A Primer-BLAST algorithm was run based on each pair of primers. Taxa Actinopterygii and Acipenseridae were used as references separately in different runs. In addition, primers were checked using local reference sequences of the complete mitochondrial genome of representatives of the genus Acipenser. The results of primer evaluation are summarized in the table Table 1. As a result, a combination of primer pairs developed on the basis of D-loop and COI fragments seems to be the most successful for error-free identification of Sakhalin sturgeon.

Sakhalin sturgeon Acipenser mikadoi (Acipenseridae): results of study and proposed measures for conservation of the species

All available data on sakhalin sturgeon Acipenser mikadoi are summarized. Its historical and modern habitats are described and their significant reduction is noted. Now the species is abundant in the Russian part of its range only — in the Tumnin River, where it is represented in commercial catches by two clearly different groups: large-sized juveniles (FL 43–68 cm) and mature fish (FL 135–169 cm). Juveniles of sakhalin sturgeon migrate during their first years, as their osmoregulatory system forms, to the lower reaches of Tumnin, to the internal estuary, and then to the Datta Bay, the Tatar Strait and the Japan Sea. When returned to the Tumnin, the spawners of sakhalin sturgeon have the length 135–169 cm (n = 29) and weight 15–36 kg. Sex ratio among the caught mature fish is 13.0 : 4 or 3.2 : 1 for females : males, on average. Fecundity of the sturgeon females sampled for artificial reproduction varied from 44.8 to 150.0 thousand eggs, on average 87.3 ± 12.1 . 103 eggs. In total, 17 mature spawners of A.mikadoi were caught in the Tumnin River in 2006–2019 for artificial reproduction (♀ = 13, ♂ = 4), 13 individuals were injected, among them 4/5 of females and 2/3 of males gave high-quality sex products. Producers of this species were distinguished by high survival during manipulations of fish breeding (100 %). Their progeny had low survival, both embryos during incubation and juveniles during rearing; the survival rate for the stage from eggs laid for incubation to juveniles with weight 3.4–7.0 g was 1.85 %. The low survival was supposedly reasoned by combination of unfavorable environmental factors and fish-breeding manipulations. Totally 11,214 juveniles of sakhalin sturgeon with weight from 3.4 to 7.0 g were released into the natural habitat (Tumnin river) in 2007, 2008, 2015, 2017, and 2019. At Anyui sturgeon fish hatchery, the broodstock of sakhalin sturgeon with 274 individuals of 5 ages is created and operated successfully. The male sturgeons in the hatchery mature at the age of 8 years. Here, 11 males of the 2007–2008 year-classes participated in the spawning in 2015–2019. Re-maturation of males was not recorded yet. For the broodstock formation in other fish hatcheries, 200 juveniles of sakhalin sturgeon were transferred to them. To preserve the species, a set of measures is proposed to strengthen its protection and to enhance its artificial reproduction, including the fry releasing into the rivers of the mainland coast, Sakhalin Island, and Japan.