Thermal requirements for growth, survival and aerobic performance of weatherfish larvae Misgurnus fossilis.

Thermal requirements of larval weatherfish Misgurnus fossilis were investigated in terms of growth, survival and aerobic performance. Growth and survival of M. fossilis larvae acclimated to five temperatures (11, 15, 19, 23 and 27° C) were measured over 25 days. In the upper temperature treatments (19, 23 and 27° C), survival of larvae was stable throughout the entire rearing period (>75%), whereas 11 and 15° C resulted in severe declines in survival (to <10%). Growth of larvae (expressed as dry mass and total length) was highest at 19 and 23° C, but significantly decreased at 27° C. Routine metabolic rate of 3 days post-hatch larvae was estimated as oxygen consumption rate (MO2 ) during acute exposure (30 min to 1 h) to seven temperatures (11, 15, 19, 23, 27, 31 and 35° C). Larval oxygen uptake increased with each consecutive temperature step from 11 to 27° C, until a plateau was reached at temperatures >27° C. All larvae of the 35° C regime, however, died within the MO2 measurement period. M. fossilis larvae show greater than expected tolerance of high temperatures. On the other hand, low temperatures that are within the range of likely habitat conditions are critical because they might lead to high mortality rates when larvae are exposed over periods >10 days. These findings help to improve rearing conditions and to identify suitable waters for stocking and thus support the management of re-introduction activities for endangered M. fossilis.

First detection of prey DNA in Hygrobates fluviatilis (Hydrachnidia, Acari): a new approach for determining predator-prey relationships in water mites.

Up to now our knowledge of water mite diet has been fragmentary. It is derived from observations in the field and laboratory or from a few selective laboratory experiments on food choice. In the present study, we were able to detect chironomid DNA in water mite bodies for the first time using molecular methods. Prey DNA was detected in virtually all Hygrobates fluviatilis (Hygrobatidae) that were fed on chironomid larvae after a starvation period of up to approximately 1 week. From the shortest interval (1 h after feeding) to the longest period after feeding (50 h) the relative amount of detected prey DNA was significantly reduced. In addition, there was a relationship between the relative amount of prey DNA and the assumed amount of the ingested prey (classified in categories of the dead prey which reflect the increasing ingestion of the mites and the decreasing body content of the prey individuals). The results of our study indicate that similar molecular analyses will be a powerful tool for diet investigations of mites from the field on various taxonomic resolutions of prey taxa. Moreover, the results of food selection experiments from the laboratory could be compared to evidence of predation by individuals from the field. For many mite taxa, especially ones which turned out to be difficult to breed in the laboratory (e.g. by unknown diet), the new methods might enable us to gain the first ever data on diet and thus may help us to consider the role of water mites in food webs more adequately in the future.

First evidence of natural reproduction of the Allis shad Alosa alosa in the River Rhine following re-introduction measures.

After stocking with larvae from the Gironde-Garonne-Dordogne population, in 2013, three young-of-the-year Allis shad Alosa alosa, probably originating from natural reproduction, were documented for the first time in a period of nearly 100 years in the River Rhine. In 2014, a further increase was observed when 57 juveniles and eight adults were caught; seven of these eight adults were derived from stocking, indicating the success of stocking measures within the framework of the EU-LIFE project.