Feeding habits of the invasive non-native black bullhead Ameiurus melas in Lake Sava (Serbia)

Abstract

The black bullhead (Ameiurus melas Rafinesque, 1820) is one of the most abundant and successful non-native fish species in European freshwaters. Recent studies indicate that it is also one of the most dominant invasive fish species in Serbian waters. The aim of this research was to determine feeding habits of the black bullhead in Lake Sava, as it is known that this species may negatively affect the native fauna through predation or competition for food/space. Black bullhead samples were collected monthly from 2009 to 2012, for four days in a row. Gastro-intestinal contents were analyzed in 2349 specimens. The analysis was done macroscopically, where possible, or under a binocular microscope. Prey categories were identified to the lowest possible taxonomic level. For the diet analysis, we used the following indices: the vacuity index, frequency of occurrence, numerical abundance, and prominence value. In addition, the seasonal trophic niche breadth was calculated according to the Shannon’s diversity index. Vacuity index ranged between 72.86% and 100%. The diet spectrum consisted of 14 different prey categories from five groups: Mollusca, Crustacea, Insecta, Teleostei, and plants. Fish were the main prey in all seasons, followed by aquatic invertebrates. Plant material and terrestrial insects were used as food in relatively small quantities. Fish-egg predation was also detected. Our research confirmed that this species is an opportunistic generalist, foraging on the most abundant and available prey. Ontogenetic diet shift was also detected. The lowest value of trophic diversity was found in the largest black bullheads, while the highest was found in the medium sized individuals. The widest niche breadth was recorded in the spring of 2011.