Food Spectrum, Trophic and Length-Weight Characteristics of Nonindigenous Suckermouth Armored Catfishes Pterygoplichthys spp. (Loricariidae) in Vietnam

The food spectrum and trophic and length–weight characteristics of an invasive species, South American suckermouth armored catfishes Pterygoplichthys spp. (Loricariidae), from lotic and lentic inland waters of Vietnam have been studied. It is found that the diet of suckermouth armored catfishes consists of plant and animal food, as well as organic detritus. According to the predominant type and pattern of feeding, suckermouth armored catfishes can be classified as detritivore gatherers (janitor). Some specimens of catfish with a high consumption of animal food have been identified. It is noted that invasive suckermouth armored catfishes can be a significant food competitor for aboriginal fish species; detritivores; and, possibly, benthophages in the lotic and lentic inland waters of Vietnam.

Ecology and distribution of the Amur Chebachok Pseudorasbora parva (Temminck et Schlegel, 1846) as a biologically invasive species in the delta and estuarine coast of the river Don

Aim. To analyze the results of ichthyological monitoring in order to identify the role of an invasive fish species, Pseudorasbora parva – known in Russia as the Amur Chebachok – in the ichthyological community of the River Don estuary littoral and delta. Material and Methods. Research work was carried out in the prodelta and estuarine watercourses of the Don delta in the period 2007‐2017. To catch the fish, we used bimtral, drag nets, gill nets and other fishing gear. Standard methods were applied to process ichthyological material. A total of 902 specimens of the Amur chebachok were examined. Results. The general characteristics of the invasive species from watercourses of the delta and from Taganrog Bay are given. Its role in the formation of ichthyofauna and its relationship with native species in new habitats has been determined. Dimensionmass indicators and other biological parameters of the species are given. Conclusion. The linear structure of the local population of the Amur chebachok consists of different size groupings corresponding to certain ages. The process of acclimatization of the Amur chebachok in the Don delta is associated with certain interactions with elements of the local biocenosis. It was proved that when there is a high number, both in pond farms and in natural water bodies, the species is an acute food competitor to juveniles of both farmed or local fish. Its rapid spread is due to the high survival rate of offspring, high environmental plasticity, rapid growth, short puberty and the migratory activity of larvae and fry.

Fish larvae as food item of planktonic predator (Chaetognatha)

Photos of predation of sagitta (Chaetognatha) to fish larvae are presented for the first time for the Black Sea. While analyzing ichthyoplankton samples obtained in May and November in 2017 (94ᵗʰ and 98ᵗʰ cruises of RV “Professor Vodyanitsky”) several sagittas were found with their guts containing fish larvae. Fish larvae seem to have been captured by sagittas in the same way as sagittas in cannibalism cases, with both folding in half at the spot of capture. The data obtained allow us to assume sagittas in conditions of high abundance of eggs and fish larvae in the plankton to be not only a food competitor of larvae and juveniles of fish, as a fodder plankton consumer, but an active predator, being able to play a significant role in the elimination of ichthyoplankton.

Intra- and inter-specific competition between Barrow's goldeneye (Bucephala islandica) and bufflehead (Bucephala albeola)

Barrow's goldeneye and bufflehead pairs defend well-delineated territories from which they exclude conspecifics. Only the male defends the territory and does so even when the female is absent. However, after the young have hatched, females of both species defend brood territories from which they exclude conspecifics. Both species are also interspecifically territorial. Barrow's goldeneye and bufflehead drakes threatened and (or) attacked 15 and 11 species, respectively. However, 55% of Barrow's goldeneye interspecific encounters were with bufflehead and 52% of bufflehead encounters were with Barrow's goldeneye. Barrow's goldeneye drakes always excluded bufflehead from their territory whereas bufflehead drakes successfully excluded yearlings, females, and unpaired Barrow's goldeneye drakes but were usually dominated by paired males. Female Barrow's goldeneye excluded all bufflehead from the brood territory and were particularly aggressive toward bufflehead broods. Food and mates are the most likely defended resources in intraspecific encounters. In interspecific encounters diving ducks were more violently attacked than dabbling ducks indicating that food may be the defended resource. Interspecific aggression of Barrow's goldeneye toward bufflehead does not appear to be misdirected intraspecific aggression but rather a directed aggression toward a food competitor and may therefore be adaptive.

Meristic variation, asymmetry, and aspects of the habitat of Culaea inconstans (Kirtland), the brook stickleback, in Manitoba

Phenetic traits were compared in 45 Culaea inconstans populations in southern Manitoba. Small body size characterized individuals of populations exposed to potentially predatory fishes. Skewing of the gill-raker distributions was greatest among populations sympatric with Umbra limi, a potential food competitor and predator. These patterns of variation are in some aspects similar to and in others contrast with those found in another stickleback, Gasterosteus aculeatus. Less fluctuating asymmetry occurred in the pectoral fin rays of stream-dwelling populations than in those of lakes. Care will be required in using fluctuating asymmetry as an indicator of environmental stress.

Life History and Ecology of American Plaice (Hippoglossoides platessoides F.) in the Magdalen Shallows

Males reach marketable size (32 cm) at age 10, and females at age 8. Sexual maturity is attained at 25 cm (age 6) for males and 41 cm (age 10) for females, and maximum spawning occurs annually from mid April to mid May. Commercial fishing has reduced the number of year-classes in the fishery from about 26 in 1957 to 17 in 1961, but has not affected the rate of growth.The main summer fishery occurs in the Chaleur Bay, Shippegan Gully, and North Bay regions in depths of 40–100 m. In winter, American plaice were most abundant in depths of 180–460 m (bottom temperature 3–6 °C), although a few immatures remained in the cold inshore waters. In spring (April), plaice were taken mostly from 75 to 150 m depths (−1.0 to 5.0 °C).Adult plaice feed mainly on molluscs and echinoderms, and young plaice on polychaetes and small Crustacea. Feeding ceases almost completely during January–March. The main food competitor of plaice in the Magdalen Shallows is the Atlantic cod, which has the same general distribution during the summer. Atlantic cod, particularly those over 78 cm long, are also the main predators of small plaice, but mortality due to cod grazing has decreased in recent years because of declining numbers of large cod.Tagging and meristic studies indicate that Magdalen Shallows plaice are a discrete stock made up of two main groups. The groups are maintained by the tendency of plaice (excluding very old individuals) to return to the same areas each summer. The northern or "Miscou–Magdalen" group includes fish of Chaleur Bay, Shippegan Gully, and Orphan Bank regions. The southern or "Cape Breton" group occurs from George Bay to St. Paul Island.