Feeding of young-of-the-year fishes of the Curonian lagoon of the Baltic sea in 2016

Results of studies on nutrition of juvenile fishes of the Curonian Lagoon of the Baltic Sea are presented. Material on young-of-the-years nutrition was collected in October 2016 during the expeditions of «AtlantNIRO» at 14 standard stations in the Curonian Lagoon. A total of 418 specimens of young-of-the-years were collected and processed. Juveniles of fishes of the Curonian Lagoon were represented by 10 species: pikeperch, bream, roach, perch, smelt, ruffe, three-spined stickleback, ninespine stickleback, bleak and sabrefish. Planktonic and benthic invertebrates formed a basis of the young-of-the-years diet. In most species of juvenile fishes, the nutritional spectra did not differ from the nutritional spectra in the range. An exception was juveniles of the ruff and ninespine stickleback, in which planktonic crustaceans predominated in the diet, while in other reservoirs they consumed bottom organisms. Only Cladocera and Copepoda were found in the diet of roach of juveniles; bottom organisms were absent. In the range of roach juveniles, bottom organisms and mollusks prevailed. The food similarity indices for juvenile fish in the Curonian Lagoon are quite high, which may indicate a tension in food relations between juveniles and (or) partial or complete overlap of their food niches. The weakening of food competition is ensured by the divergence of daily dietary peaks. Three-spined and nine-spined sticklebacks as well as a sabrefish and sticklebacks have the closest food spectrum. On the contrary, sabrefish and bream have a different food spectrum. The peculiarity of feeding of pikeperch juveniles in 2016 was the lack of transition to predatory nutrition.

FORMATION OF «FALSE ANNUAL RINGS» ON SCALES OF JUVENILE COHO SALMON ONCORHYNCHUS KISUTCH IN LAKE KURAZHECHNOYE (KAMAKOVSKAYA LOWLAND — KAMCHATKA RIVER BASIN)

During spring-summer flood (in mid May — July), transit underyearlings of coho salmon, having or having no scales, migrate to Lake Kurazhechnoye at the lower Kamchatka River, where resident coho salmon never spawn. In this case, additional zones of closely–spaced sclerites (ZCS) can be formed on their scales because of feeding change (additional ZCS of the 1st type). Seasonal growth restarts and annual zone of close sclerites (annual ring) forms in May (or in early June for a part of juveniles) on scales of yearlings and elder coho salmon wintered in Lake Kurazhechnoye. In late July — August or sometimes later, other additional ZCS could form on the scale of juvenile coho salmon (ages 1+ and 2+) in the lake (additional ZCS of the 2nd type) because of their switching to feeding by fish (ninespine stickleback Pungitius pungitius, threespine stickleback Gasterosteus aculeateus, and smelt Hipomesus olidus). Rate of the sclerites forming was examined for the coho juveniles of age 1+ in Lake Kurazhechnoye in 2001 and evaluated as 8.52 days/sclerite, on average (one sclerite was formed in 9.18 days between June 13 — July 5 but in 7.86 days between July 5–23).

The cestode parasite Schistocephalus pungitii: castrator or nutrient thief of ninespine stickleback fish?

SUMMARYIn this investigation, the host–parasite relationship of ninespine stickleback fish Pungitius pungitius and the cestode parasite Schistocephalus pungitii was studied using samples from Dog Bone Lake, Kenai Peninsula, Alaska, to test the hypothesis that S. pungitii is a castrator of ninespine stickleback. Infected, adult females of all sizes (ages) were capable of producing clutches of eggs. S. pungitii had a negative effect on the ability of host females to produce a clutch, which was related to increasing parasite:host mass ratio (parasite index, PI). Among infected females with egg clutches, both clutch size and egg size were reduced; and the reduction increased with greater PI. The results of this study are consistent with the hypothesis that S. pungitii causes host sterility as a result of simple nutrient theft and is not a true castrator as hypothesized in earlier reports. The degree of parasite-induced sterility appears to vary among populations of the ninespine stickleback, perhaps reflecting differences in resource availability. Populations of ninespine stickleback appear to show a greater reduction in host reproductive capacity with PI than populations of the threespine stickleback infected by Schistocephalus solidus, possibly owing, in part, to the length-adjusted somatic mass of the threespine stickleback being greater.

To what extent do human-altered landscapes retain population connectivity? Historical changes in gene flow of wetland fish Pungitius pungitius

Understanding how human-altered landscapes affect population connectivity is valuable for conservation planning. Natural connectivity among wetlands, which is maintained by floods, is disappearing owing to farmland expansion. Using genetic data, we assessed historical changes in the population connectivity of the ninespine stickleback within a human-altered wetland system. We predicted that: (i) the contemporary gene flow maintained by the artificial watercourse network may be restricted to a smaller spatial scale compared with the gene flow preceding alteration, and (ii) the contemporary gene flow is dominated by the downstream direction owing to the construction of low-head barriers. We evaluated the potential source population in both timescales. Seventeen studied populations were grouped into four genetically different clusters, and we estimated the migration rates among these clusters. Contemporary migration was restricted to between neighbouring clusters, although a directional change was not detected. Furthermore, we consistently found the same potential source cluster, from past to present, characterized by large amounts of remnant habitats connected by artificial watercourses. These findings highlight that: (i) artificial connectivity can sustain the short-distance connectivity of the ninespine stickleback, which contributes to maintaining the potential source populations; however, (ii) population connectivity throughout the landscape has been prevented by agricultural developments.