Abstract
The weatherfish (Misgurnus fossilis) is a species that is tolerant of unfavourable environmental conditions and can survive low dissolved oxygen concentrations and high water temperatures. Although this species occurs across almost the whole of Europe, and is protected in many countries, relatively little is known regarding its ecology. To determine the diet of weatherfish, 120 individuals from an artificial drainage canal in central Poland were collected in two seasons (spring and late summer) with contrasting abiotic condition (oxygen concentration, water temperature and transparency). Analysis of gut fullness showed that weatherfish consumed a greater quantity of food in spring (0.92 ± 0.90) compared with summer (0.20 ± 0.26). Contrary to other cobitid taxa, weatherfish fed actively during daytime in both seasons. An estimate of the importance of each dietary component indicated that the most important food categories were chironomids, copepods, Asellus aquaticus and detritus. SIMPER analysis indicated that these four categories together constituted over 65.8% of cumulative dissimilarity in the diet between seasons. Additionally, trophic niche breadth differed significantly between seasons. The study demonstrated that the weatherfish is an opportunistic feeder, consuming large quantities of detritus despite possessing a gut morphology that is atypical of a detritivore. The quantity of detritus in the gut of weatherfish was positively associated with fish total length and varied seasonally, with a greater quantity of detritus in the diet in late summer. These results demonstrate the importance of detritus as a source of energy, particularly during periods of scarcity of alternative prey categories.
Highlights
In the temperate zone, freshwater ecosystems are characterized by natural variation in environmental conditions resulting, inter alia, from climate seasonality[1,2]
Dissolved oxygen concentrations in May were over 12 mg l−1, while they never exceeded 3 mg l−1 in August (Table 1)
In May the highest fullness coefficient (FC) values were observed at noon and differed significantly from the values in the afternoon (i.e. 18.00)
Summary
Freshwater ecosystems are characterized by natural variation in environmental conditions resulting, inter alia, from climate seasonality[1,2]. Low oxygen concentrations result from elevated water temperature, accompanied by an increase in water conductivity and decomposition of organic sediments on the substrate[6,7] Under these conditions there is often a decrease in macroinvertebrate biomass, mainly as a consequence of the loss of oxygen-sensitive taxa and thereby a scarcity of the food resources for fish[8,9,10]. M. fossilis is a small, benthic freshwater cobitid, native to almost all of Europe It inhabits stagnant freshwaters, such as oxbow lakes and ponds, as well as slow-flowing rivers, canals and drainage ditches that are overgrown with dense vegetation[15]. This fish species usually occurs on a sandy substrate covered with a thick layer of mud and organic matter[16,17]. Three specific questions were addressed: (1) whether there is a diel feeding activity in weatherfish; (2) whether there is a seasonal pattern in diet composition, and (3) whether detritus makes a significant contribution to the diet, and whether this varies seasonally
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