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.

Novel picornavirus (family Picornaviridae) from freshwater fishes (Perca fluviatilis, Sander lucioperca, and Ameiurus melas) in Hungary

In this study, a novel picornavirus (perchPV/M9/2015/HUN, GenBank accession no. MW590713) was detected in eight (12.9%) out of 62 faecal samples collected from three (Perca fluviatilis, Sander lucioperca, and Ameiurus melas) out of 13 freshwater fish species tested and genetically characterized using viral metagenomics and RT-PCR methods. The complete genome of perchPV/M9/2015/HUN is 7,741 nt long, excluding the poly(A) tail, and has the genome organization 5’UTRIRES-?/P1(VP0-VP3-VP1)/P2(2A1NPG↓P-2A2H-box/NC-2B-2C)/P3(3A-3BVPg-3CPro-3DPol)/3’UTR-poly(A). The P1, 2C, and 3CD proteins had 41.4%, 38.1%, and 47.3% amino acid sequence identity to the corresponding proteins of Wenling lepidotrigla picornavirus (MG600079), eel picornavirus (NC_022332), and Wenling pleuronectiformes picornavirus (MG600098), respectively, as the closest relatives in the genus Potamipivirus. PerchPV/M9/2015/HUN represents a potential novel fish-origin species in an unassigned genus in the family Picornaviridae.

Morphometric and genetic evidence for cryptic diversity in Gyrodactylus (Monogenea) infecting non-native European populations of Ameiurus nebulosus and A. melas

Gyrodactylid parasites were observed on non-native populations of North-American freshwater catfishes, Ameiurus nebulosus and Ameiurus melas (Siluriformes: Ictaluridae), at several sites in the Elbe River basin, Czech Republic, Europe. Using a combination of morphological and genetic analyses, the parasites infecting A. nebulosus were determined to be Gyrodactylus nebulosus, a North American parasite co-introduced to Europe along with its Ameiurus fish hosts. Subtle morphometrical differences, as well as seasonal variations, were observed among parasites collected from A. nebulosus and A. melas. The host-related variation was further supported through genetic analysis of the partial 18S rDNA, ITS1-5.8S-ITS2 and COI, showing 0.2, 3.0 and 4.8% divergence, respectively. Consistent genetic differences indicated there were two distinct genotypes. Subtle morphological differences associated with the shape of sickle toe, anchor root and ventral bar membrane, according to host species, also supported the description of a new cryptic species, Gyrodactylus melas n. sp., infecting A. melas. Multivariate morphometrical analysis of haptoral hard parts showed significant differences between the anchor lengths of G. nebulosus and G. melas n. sp. However, the measurements of the haptoral hard structures partially overlapped between species, limiting the usage of these parameters for species delineation.

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.