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First report on the importance of alien gobiids in the diet of native piscivorous fishes in the lower Vistula River (Poland) [commun.]

Płąchocki D., Kobak J., Kakareko T.

Oceanological and Hydrobiological Studies

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2012

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Vol. 41, No. 2

83-89

EN

We conducted a snapshot study to check the importance of non-native Ponto-Caspian gobies (monkey and racer goby) in the diet of native obligate (northern pike, pikeperch) and facultative (Eurasian perch) predators in the Vistula River 3-4 years after the appearance of aliens. In total 71 fish with non-empty stomachs, taken randomly from net catches from various parts of the river were analyzed, including 32 pike, 20 pikeperch and 19 perch specimens. We found that gobiids prevailed in the diet of smaller (<30 cm standard length, SL) individuals of pike and pikeperch, as well as larger (>15 cm SL) specimens of perch, although the effect of predator size on the presence of gobiids in the diet was not significant in the case of perch. Our results indicate that gobiids as a prey fish can stimulate considerable changes in local food webs, which require further studies.

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Peculiarities of macrozoobenthos in the offshore zone of a small artificial post-gravel pit reservoir

Żbikowski J., Kobak J.

Oceanological and Hydrobiological Studies

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2010

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Vol. 39, No.1

39-59

EN

The offshore macrozoobenthos and selected environmental parameters were studied in a small artificial reservoir, created through sand and gravel extraction. The results are rather surprising. Despite the shallow depth and good wind exposure of the reservoir, a thermal and oxygen stratification developed in the summer, causing hypoxic conditions near the bottom, even though the organic matter content in the sediments was <5%. Furthermore, despite the high fish abundance, chaoborids prevailed in zoobenthos, while Tanytarsus sp. and Chironomus sp. co-dominated among chironomids. This study attempts to explain the observed phenomena, though the presented hypotheses still need further confirmation.

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Relationships between the occurrence of Chaetogammarus ischnus (Stebbing, 1898) and Pontogammarus robustoides (G. O. Sars, 1894) (Crustacea, Amphipoda) in a lowland Polish dam reservoir

Żytkowicz J., Kobak J.

Oceanological and Hydrobiological Studies

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2008

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Vol. 37, No.2

39-50

EN

Populations of Chaetogammarus ischnus and Pontogammarus robustoides living in the middle part of the Włocławek Dam Reservoir (on the lower Vistula River, central Poland) were studied. The two species coexisted at offshore sites of the reservoir, with P. robustoides being much more abundant than C. ischnus. In samples collected from the bare bottom of the reservoir (sandy or covered by zebra mussel shells) and macrophytes a negative relationship between the two species was observed: C. ischnus occurred in high numbers in those samples in which abundance of P. robustoides was low. This phenomenon is postulated as resulting from the larger size and more predatory nature of P. obustoides, limiting the occurrence of C. ischnus.