Demographic and Life History Characteristics of Black Bullheads Ameiurus melas in a North Temperate USA Lake

Black bullheads Ameiurus melas are an environmentally tolerant omnivorous fish species that are found throughout much of North America and parts of Europe. Despite their prevalence, black bullheads are an infrequently studied species making their biology, ecology, and life history poorly understood. Although limited information has been published on black bullheads, evidence suggests that bullheads can dominate the fish biomass and have profound influences on the fish community in some north temperate USA lakes. The goal of our study was to provide additional information on black bullhead population demographics, growth rates, life history characteristics, and seasonal diet preferences in a northern Wisconsin lake. Using common fish collection gears (fyke netting, electrofishing), fish aging protocols, fecundity assessments, and diet indices, our results suggested that black bullheads exhibited relatively fast growth rates, early ages at maturity, moderate fecundity, and a diverse omnivorous diet. Due to these demographic and life history characteristics, black bullheads have the potential to dominate fish community biomass in their native and introduced range. Results from our study may inform the management of black bullhead as native and invasive species.

Seasonal feeding habits and ontogenetic diet shift of black bullhead (Ameiurus melas) in Lake Sava (Serbia)

The black bullhead is an invasive species that forms dense populations and has a negative impact on the native ichthyofauna. Recent studies indicate that it is one of the most dominant invasive fish species in Serbian waters. Feeding habits based on stomach contents of individuals caught in Lake Sava were analyzed as a first step towards evaluating its possible negative impact on the native fish fauna of the lake. The following indices for diet analysis were applied: vacuity index, frequency of occurrence, numerical abundance and prominence value. Trophic niche breadth and seasonal trophic diversity were calculated using the Shannon?s index. The diet spectrum comprised 16 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. Predation on fish eggs was also detected. Our research confirmed that this species is an opportunistic generalist. An ontogenetic diet shift was also detected. The lowest value of trophic diversity was found in age 1+ individuals (H=1.39), while the highest was found in age 3+ individuals (H=2.00). The widest niche breadth was recorded in spring 2011 (H=2.12).

Can Invasiveness in Freshwater Fishes Be Predicted From Life-History Traits?

We review a model we developed in 2007 to predict the invasion potential of an introduced population, based on the relationship between juvenile growth (mean total length at age 2) and mean age-at-maturity, and test the model with data from 75 non-native populations of pumpkinseed Lepomis gibbosus in nine countries of Europe and western Asia. The database used to construct the model was derived from a mix of primary and secondary data collected between 1981 and 2016. Based on number of specimens collected or catch-per-unit-effort data, and/or comments by the original authors, populations were classified a priori as “invasive” or “non-invasive.” The plot of the proposed model placed populations in three invasiveness categories (non-invasive, transitional, invasive). Of those predicted by the model to be invasive, only 57% were correct with regard to their a priori classification, a result that was not statistically significant. For populations predicted by the model to be non-invasive, 70% were correct with regard to their a priori classification when “transitional” were grouped with non-invasive (P = 0.0024), and 64% were correct when “transitional” were excluded from the test (P = 0.12). Applications of the model to two other non-native freshwater fishes (black bullhead Ameiurus melas and crucian carp Carassius carassius) are also discussed. The lack of stronger statistical support for the model may have been the result of using life-history traits from the populations after they were introduced, as the source populations were unknown, as well as to shortcomings in the dataset that could affect a priori and modeled classifications. We conclude that such life-history models can be useful for predicting invasiveness status in non-native freshwater fishes, though the basis of the predictions, statistical or heuristic, will depend on the size and quality of the underlying life-history database.

Behavioural and morphological changes in fish exposed to ecologically relevant boat noises

There is increasing concern about the effect of underwater noise on fish due to rising levels of anthropogenic noise. We performed experiments on the black bullhead (Ameiurus melas), a species with known hearing specializations and located within the Laurentian Great Lakes where there is considerable commercial and recreational boat traffic. We tested and compared physiology (baseline cortisol), behaviour (activity, sheltering), and morphology (ciliary bundles of hair cells) of bullhead to boat noise. At 140 dB re 1 μPa (−54.84 dB re 1 m·s−2), we saw clear behavioural effects in terms of both activity and sheltering levels despite no obvious morphological or physiological stress. Following both short- and long-period acute exposure to higher — but environmentally relevant — noise levels, bullhead were less active and sheltered more and also exhibited a decrease in ciliary bundles. These results suggest that there are sublethal effects of anthropogenic noise on fish behaviour and ciliary bundles, which may have direct implications on population health. Moreover, commonly used metrics such as stress hormones may not always offer the most relevant biomarker of the response to anthropogenic boat noise.

What Environmental Conditions Reduce Predation Vulnerability for Juvenile Colorado River Native Fishes?

The incompatibility of native Colorado River fishes and nonnative warm-water sport fishes is well documented, with predation by nonnative species causing rapid declines and even extirpation of native species in most locations. In a few rare instances, native fishes can survive and recruit despite the presence of nonnative warm-water predators, indicating that specific environmental conditions may help reduce predation vulnerability. We experimented with turbidity, artificial blue water colorant (artificial turbidity pond treatment), woody debris, rocks, and aquatic vegetation in a laboratory setting to determine whether any of these types of cover could reduce predation vulnerability and confer survival advantages for juvenile Bonytail Gila elegans (mean = 70 mm total length), Roundtail Chub Gila robusta (mean = 35 mm total length), Humpback Chub Gila cypha (mean = 67 mm total length), and Razorback Sucker Xyrauchen texanus (mean = 74 mm total length). We exposed selected species of juvenile native fishes to predation by adult Largemouth Bass Micropterus salmoides, Smallmouth Bass Micropterus dolomieu, Green Sunfish Lepomis cyanellus, Flathead Catfish Pylodictis olivaris, and Black Bullhead Ameiurus melas in overnight trials. Razorback Suckers served as prey in trials conducted with Largemouth Bass and Black Bullhead. Bonytail served as prey in trials conducted with Largemouth Bass and Flathead Catfish. Roundtail Chub served as prey in trials conducted with Smallmouth Bass and Green Sunfish. We matched sizes of predator and prey so that the maximum body depth of the prey never exceeded 40% of the maximum anatomical gape of the predators. Turbidity of 500 nephlometric turbidity units reduced effectiveness of sight-feeding predators such as Largemouth Bass, Smallmouth Bass, and Green Sunfish by up to 50% but also increased predation vulnerability to non–sight-feeding predators (Flathead Catfish and Black Bullhead) by up to 55%. Turbidity was the only treatment that significantly altered predation mortality of native fish. These results may help explain recent patterns of wild juvenile native fish recruitment to adult life stages at the Colorado River inflow in to Lake Mead and at the inflow of the San Juan River into Lake Powell. Both areas possess abundant introduced predatory fishes but are also very turbid.

Genome Sequence of a Novel Alloherpesvirus Isolated from Glass Catfish ( Kryptopterus bicirrhis )

ABSTRACT The 149,343-bp genome of silurid herpesvirus 1, which was isolated in Thailand from glass catfish, was sequenced. The genome was most closely related to that of ictalurid herpesvirus 2, which infects black bullhead catfish. To our knowledge, this was the first silurid catfish alloherpesvirus genome to be sequenced.