On the Taxonomic Status of the Red Icefish Channichthys rugosus (Notothenioidei: Channichthyidae) from the Kerguelen Islands (South Ocean)

The presented work is the final part of the taxonomic revision of the Antarctic icefishes of the genus Channichthys Richardson, 1844 (Notothenioidei: Channichthyidae) from the Kerguelen Islands, the species composition of which was discussed until recently. Based on the morphological study of all available specimens from the ZIN and BMNH collections (including the holotype), a comprehensive redescription of the Red icefish Channichthys rugosus Regan, 1913 from the waters of the Kerguelen islands (South Ocean) was carried out, including external morphology, seismosensory system, gill apparatus, and axial skeleton. As a result, new diagnostic features of Red icefish were discovered and previously known ones were clarified, which made it possible to confirm the species validity. Comparison with other valid species icefishes was done. Channichthys rugosus differs from Ch. rhinoceratus Richardson, 1844 by a high anterior dorsal fin, the fin membrane of which reaches the apexes of its longest rays (does not reach in Ch. rhinoceratus), as well as a narrow and concave interorbital space (compared to the wider and flat one), by stronger granulation and a uniform reddish body color (dark spotted-marble in Ch. rhinoceratus). Channichthys rugosus differs from Ch. velifer Meissner, 1972 by the number of rays in the first dorsal fin (7–9 versus 9–12) and pectoral fin (18–20 versus 20–21), the presence of bone plaques in the proximal part of the medial lateral line (absent in Ch. velifer), and monochromatic reddish body coloration (spotted in Ch. velifer). Channichthys rugosus differs from Ch. panticapaei Shandikov, 1995 by the presence of only 1 row of gill rakers on the first gill arch (2 rows in Ch. panticapaei) and by light coloration (brownish-black in Ch. panticapaei).

Redescription of the unicorn icefish Channichthys rhinoceratus Richardson (Notothenioidei: Channichthyidae) with synonymization of three similar species

On the basis of a comprehensive study of the external morphology, seismosensory system and gill apparatus, a revision of the Kerguelen icefishes of the genus Channichthys Richardson, 1844 (Notothenioidei: Channichthyidae) was carried out in order to confirm or refute the validity of a questionable species of this genus. The need for the presented study arose due to the lack of an unambiguous accepted opinion of various specialists about the exact species composition of this genus of Antarctic fish. The studied sample included 40 specimens of the type species of this genus, unicorn icefish Channichthys rhinoceratus Richardson, 1844 from the collection of the Zoological Institute RAS and holotypes of 3 species, Aelita icefish Ch. aelitae Shandikov, 1995, green icefish Ch. mithridatis Shandikov, 2008 and robust icefish Ch. richardsoni Shandikov, 2011, from the Zoological collection of the National Museum of Natural History NAS of Ukraine. The classical technique was used for the morphological study of fish with subsequent comparative analysis of the data obtained. As a result, Ch. rhinoceratus is redescribed, highlighting the most important diagnostic characters. Three similar species (Ch. aelitae, Ch. mithridatis and Ch. richardsoni) are place in synonymy of the latter. Basing on the results of this and our previous species revisions of Channichthys, a key for identification has been compiled, which includes diagnostic features of all four valid icefishes, Ch. rhinoceratus, Ch. velifer, Ch. rugosus and Ch. panticapaei.

THE INFLUENCE OF THE HIGH CONTENT OF Cа2+, Mg2+ AND Nа+ ON VARIABILITY OF THE PORES NUMBER IN LATERAL LINE CRANIAL CANALS OF ROACH FINGERLINGS

In a five-month aquarium experiment, roach Rutilus rutilus (Linnaeus, 1758) fingerlings were grown under different hydrochemical conditions. Roach eggs were collected during the spawning period in the shallow coastal waters of a small isolated and unpolluted pond and placed in laboratory for subsequent incubation. Hatched early larvae after switching to exogenous nutrition were divided into four groups for further development in control hydrochemical condition and in the water with a total mineralization increased twice relative to the control due to the addition of calcium, magnesium or sodium chloride salts. At the end of the experiment, roach fingerlings grown in the three groups in conditions of increased water mineralization differed statistically significantly from their coevals in the control group by a smaller average number of pores in the lateral line canals located on some paired dermal bones of the head. Also, these three groups of roach in comparison with the control group were characterized by an increase in the dispersion of the fluctuating asymmetry of the total values of the studied bilateral counting features. The obtained results are explained in the light of the possible influence of the above biologically significant cations on the morphogenesis of the cranial seismosensory system during the early individual development of fishes.

On the taxonomic status of Eumicrotremus eggvinii Koefoed, 1956, Eumicrotremus phrynoides Gilbert et Burke, 1912 and Lethotremus muticus Gilbert, 1896 (Cyclopteridae, Cottoidei) in the light of data on the morphological variability of Eumicrotremus pacificus Schmidt, 1904

A comparison was performed of the morphological variability of the spotted lumpsucker Eumicrotremus pacificus Schmidt, 1904, E. spinosus (Fabricius, 1776), whose synonymy recently included E. eggvinii Koefoed, 1956, and E. gyrinops sensu Stevenson et al., 2017, recently established as the senior synonym for E. phrynoides Gilbert et Burke, 1912 and Lethotremus muticus Gilbert, 1896. Based on a number of morphological differences between E. spinosus and E. eggvinii, corresponding to differences between young and spawning males E. pacificus, it was suggested that individuals E . eggvinii may be nesting males of E. spinosus. It was established that the range of variability of a number of morphological characters of E. gyrinops exceeds that of E. pacificus, which suggests its complex nature. Notable differences in the ratio of the size of the anterior and posterior nostrils, the size of the chin tubes of the seismosensory system and the shape of bone plaques between E. phrynoides and E. gyrinops indicate the validity of E. phrynoides. The absence of an external skeleton in both males and females of L. muticus, unlike other species of the genus Eumicrotremus, allows us to conclude that L. muticus is also a valid species.

Variability of the countable features of head seismosensory system in different species of freshwater fishes and their dependence on hydrochemical factors

Countable morphological features in individuals of three mass species of fishes – roach, perch and crucian carp, living in small ponds of the Central-Eastern part of Udmurtia – were studied. The number of holes of seismosensory channels in some paired cover bones of the head skeleton of the caught fishes was counted and the sum of the values of these countable features (ΣSS) was calculated with averaging for the left and right sides. The total mineralization of water was also measured in the investigated reservoirs and the content of calcium and magnesium ions was estimated in the water. For all three fish species, one trend of interpopulation variability was revealed: with an increase of the concentration of Mg2+ in fresh water, the average value of ΣSS decreased in fish individuals from the studied populations. Statistically significant differences in mean values and frequency distributions of discrete variants of this seismosensory feature were observed for populations of roach, perch and crucian carp, living in water bodies with the greatest differences in the content of magnesium. In addition to full-scale research, laboratory experiments on aquarium cultivation of juvenile perch and roach in various hydrochemical conditions were carried out. Formed in fresh water with a high content of Mg2+, perch and roach juveniles had a smaller number of holes of seismosensory channels in some head bones in comparison with juveniles from the control groups and adult individuals of these fish species in reservoirs, where fertilized fish eggs for incubation were taken. Increased concentrations of Na+ did not have a similar effect on the formation of the studied signs. To explain the observed ontogenetic effects, we consider the possibility of direct influence of magnesium ions on the rate of larvae development of the freshwater fishes, as well as indirect influence on their morphogenesis of the competitive biochemical relations of this element with calcium.