Biology and fishery of pond smelt Hypomesus olidus in the Amur River basin

In the Amur River, there are two ecological forms of pond smelt Hypomesus olidus: anadromous and freshwater. Generalized information about biology and fishery of the anadromous form of pond smelt is presented. The smelt migrate to the Amur for spawning in winter and spring, and for wintering in autumn. The most remote point of their spawning migration is Bolbinsky cliff (375 km from the mouth). The spawning herd is represented by three age groups: 2-, 3-, and 4-year-old fish; the two-year-old fish are the most numerous. The sex ratio of spawning smelt is close to 1 : 1, though females prevail slightly. Body length of the pubescent fish ranges from year to year from 7.6 to 13.2 cm, body weight — from 3.05 to 16.04 g; females are slightly larger than males. Absolute fecundity of pond smelt ranges from 0.7 to 12.4 thousand eggs, relative fecundity — from 199 to 1287 eggs/g. During migration to the spawning grounds, the smelt practically do not feed, but they go to active feeding after spawning. Pond smelt is a popular object of fishery in the Amur basin: on average 1569.2 t were caught annually in 2010–2019, during the spawning migration, mainly in the lower Amur River between Nikolayevsk-on-Amur and Bogorodskoe.

Sockeye salmon (Oncorhynchus nerka) return after an absence of nearly 90 years: a case of reversion to anadromy

We document the recent reappearance of anadromous sockeye salmon ( Oncorhynchus nerka ) that were thought to have been extirpated by the construction of hydroelectric dams on the Coquitlam and Alouette rivers in British Columbia, Canada, in 1914 and 1927, respectively. Unexpected downstream migrations of juveniles during experimental water releases into both rivers in 2005 and 2006 preceded upstream return migrations of adults in 2007 and 2008. Genetic (microsatellite and mitochondrial DNA) markers and stable isotope (δ34S and 87Sr/86Sr) patterns in otoliths confirm that both the juvenile downstream migrants and adult upstream migrants were progeny of nonanadromous sockeye salmon (kokanee) that inhabit Coquitlam and Alouette reservoirs. Low genetic diversity and evidence of genetic bottlenecks suggest that the kokanee populations in both reservoirs originated from relatively few anadromous individuals that residualized after downstream migration was largely prevented by the construction of dams. Once given an opportunity for upstream and downstream migration, both populations appear capable of reverting to a successful anadromous form, even after 25 generations.

Age at First Maturity and the Early Expression of Oocyte Recruitment Processes in Two Forms of Atlantic Salmon (Salmo salar)and Their Hybrids

The two pure lines and the reciprocal hybrids between an early maturing dwarf form of landlocked Atlantic salmon (Salmo salar) and a later maturing anadromous form were reared in captivity for a minimum period of 2.5 yr. Despite similar growth rates, 90% of female parr of the dwarf landlocked strain matured at age 2+ yr (fork length 15 cm), while no females of the anadromous form matured at this time. The weight of the ovary differed in the two pure forms at age 0+ and the numbers, size, and stages of previtellogenic oocytes also differed at age1+. Ovarian patterns of development and the time of onset of sexual maturation in the hybrid forms appeared intermediate to that of the parental forms. The implications of genetically controlled factors influencing rates of sexual maturation, growth, smoltification, and subsequent fecundity are discussed.

Osmoregulation in Juvenile and Adult Lampreys

Nonparasitic lampreys are well adapted for a freshwater existence but are less tolerant of salt water than representatives of the parasitic species. Anadromous feeding juvenile sea lampreys, Petromyzon marinus, are able to control serum osmotic and ionic concentrations in all salinities between 0 and 34‰. Juveniles of the anadromous European river lamprey, Lampetra fluviatilis, are slightly less tolerant of salinity change. The transition of P. marinus to a landlocked existence has resulted in a reduction in the capacity for marine osmoregulation. Tolerance to salt water among landlocked P. marinus is related directly to size emphasizing the advantage afforded through a reduction of surface area relative to body volume. Changes in serum osmolality are primarily the result of corresponding shifts in sodium and chloride ions. Changes in chloride are not accompanied by an equivalent shift in sodium suggesting that the relationship between the two ions is not passive. Regulation of sodium by landlocked P. marinus is not precise as that exhibited by the anadromous form particularly in the higher salinities. Nontrophic upstream migrant lampreys display a reduction in their marine osmoregulatory mechanisms and a restoration of the freshwater osmoregulatory apparatus. Freshwater osmotic and ionic regulation deteriorates in spent adult lampreys.Key words: blood, ionic regulation, osmotic regulation, parasitic and nonparasitic lampreys, salinity, life cycle

Mate selection in threespine sticklebacks (Gasterosteus)

Earlier studies suggest that the freshwater form of the threespine stickleback (Gasterosteus aculeatus) may be reproductively isolated from the anadromous form. In this study, assortative mating is examined as a possible isolating mechanism between the two forms. Mate selection tests were conducted in which (1) courting males were simultaneously exposed to receptive females of both forms, and (2) receptive females were simultaneously exposed to both forms of courting males. The results demonstrate clearly that in choice situations matings between similar phenotypes are more likely than matings between dissimilar phenotypes.

Effect of pituitary homotransplants on peripheral target organs in intact threespine sticklebacks, Gasterosteus aculeatus L. form trachurus

The activity of pituitary homotransplants in the anadromous form (trachurus) of the threespine stickleback, Gasterosteus aculeatus L. was investigated by examining the structure of the thyroid, interrenal, gonad, and in situ pituitary; the melanophore index was also measured.The thyroid gland was markedly more active and the in situ thyrotrophs more granulated in the recipient fish when compared with the sham-operated animals. Similarly, the interrenal nuclear index was slightly (but significantly) larger in the recipient fish and there was a concomitant partial regression of the in situ pituitary corticotrophs.There was no difference between the structure of the gonads in the two groups although the in situ gonadotrophs were apparently smaller and less well granulated in the recipient fish.The melanophore index was significantly lower in recipient sticklebacks.In situ prolactin-secreting cells, somatotrophs, and neurointermediate lobes were similar in recipient and sham-operated animals.