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Invertebrate reproduction in astatic water bodies : egg number - body weight relationship in Viviparus viviparus (L.) from oxbow lakes

Jakubik B.

Polish Journal of Ecology

2012

Vol. 60, nr 2

363-374

Reproduction is the most important factor in population dynamics and invading freshwater habitats by Viviparus viviparus. This is largely associated with ovoviviparity of these snails. Some traits like steered reproduction, the appearance of young snails during the whole year, protection of embryos by female and delayed reproduction were fixed by natural selection as adaptations increasing the chance for progeny survival. In variable habitats like oxbow lakes seasonally joined to the river channel, Viviparidae start reproducing in the early stage of their life hence increasing a chance for population to survive. Studies on fecundity, embryonic development of V. viviparus and the relationships between these parameters and females. body size and weight, were carried out in oxbow lakes periodically connected to the river (the Bug River, Central Poland). The Bug River is one of a few European rivers which preserved their nearly natural character. No larger hydrotechnical works have been made in its valley, therefore, the river flows in a natural, meandering channel and forms numerous oxbow lakes. The surrounding of studied oxbow lakes is flat and of lowland character with mixed land use structure (arable lands, grasslands, settlements). Oxbow lakes are fed by the runoff from flood terrace, hence their waters are more fertile than those of the river. Two lakes were selected: Lake Szumin, area 17 ha, Lake Wywłoka - area 23 ha. Maximum depth of both lakes is ca 3 m. Samples of V. viviparus were collected in the years 2003-2007 with a bottom drag during the successive seasons from five sites in each oxbow lake. The embryos were found in females of the II (8.1-12.0 mm of width and height), III (12.1-20.0 mm width and 12.1-25.0 mm height) and IV (over 25.0 mm height and over 20.0 mm width) size classes. Three developmental stages were distinguished in embryonic growth: the oval transparent egg capsules (called the youngest embryos), egg capsules with visible contour of a shell (called medium embryos) and snails with a shell (the oldest embryos). The youngest growth stages of embryos (in a form of oval transparent egg capsules) dominated in all size classes of females. Medium growth stages (egg capsules with visible outlines of the shell) and the oldest ones (with shell) were represented in smaller proportion. The highest number of the youngest embryos per female were found in females of the II size class. The proportions of the embryo growth stages varied seasonally. The number of embryos per female and the degree of their development increased with the increase of shell (height, width, dry weight) and body (dry weight) parameters. High fecundity of the youngest females of V. viviparus is probably an adaptation to unstable habitat conditions of oxbow lakes.

Exposure of whitefish (Coregonus lavaretus) eggs to native or chemically spiked sediments from Lake Thun does not lead to abnormal gonad development

Bernet D., Wahli T., Gerecke A., Segner H.

Environmental Biotechnology

2011

Vol. 7, No. 1

17-29

A high number of whitefish, Coregonus lavaretus, from Lake Thun, Switzerland, display gonad malformations. We tested the hypothesis that exposure to sediment-borne contaminants during the embryonic life results in the development of malformed gonads later in ontogeny. The investigated contaminants were 2,4,6-trinitrotoluene (TNT), which may leak from residues in the lake sediments as consequence of former ammunition dumping into Lake Thun, as well as sulfonated naphthalene formaldehyde condensates (SNFC), which are introduced into the lake from wastewater disposals of a nearby tunnel construction site. Experimentally, whitefish eggs were exposed during 52 days from fertilization until hatching to a) an artificial sediment (control), b) an artificial sediment spiked with TNT (0.5mg*kg-1 dry weight), c) SNFC compounds dissolved in water (3µg*l-1 of each naphthalene-1-sulphonate, naphthalene-2-sulphonate, naphthalene-1,5-disulphonate, naphthalene-2,7-disulphonate), and d) sediment from Lake Thun sampled in an ammunition dumping area. To mimic in situ exposure of the eggs to the sediment-water-interface under laboratory conditions, we developed a novel contact incubation technique. After hatching, fish were reared in tap water for three years until they reached sexual maturity, and were then examined for the presence of gonad malformations. No malformations were observed in the control, in the TNT and SNFC treatment groups. In fish incubated during the embryonic stage on Lake Thun sediment, 2 out of 117 adult males (1.7%) displayed malformed gonads, which is significantly lower than levels of gonad malformations in wild whitefish from Lake Thun (on average 29% in males, 12% in females). The results from our experiment provide no evidence that sediment contamination with TNT or SNFC compounds is a causative factor for the induction of gonad malformations in Lake Thun whitefish.