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Two species of fish, Carassius auratus and Ictalurus nebulosus, were subjected to cold acclimation regimes. Acclimation temperatures were slowly lowered to 3°c, then held for a period of time. At various times during this regime, fish were taken out and allowed to spend time in a temperature gradient to determine their preferred temperatures. Carassius were left in the gradient just long enough to determine a measure of the acute temperature preference, while Ictalurus were left in the temperature gradient for longer periods of time to observe any changes that might occur as the fish adjusted to selected temperatures. In both species of fish, lower acclimation temperatures and increased time spent at low temperatures caused a preference for lower temperatures in the gradient.

The accumulation of persistent contaminants is a significant issue for the health of aquatic environments. This study aims to determine the effects of polycyclic aromatic hydrocarbons (PAH) on the stress response of fish by monitoring plasma cortisol levels and the expression of key hypothalamic-pituitary-interrenal (HPI) stress axis regulators. Injection of benzo(a)pyrene (BaP), a ubiquitous PAH, induced a differential dose- and time-dependentcortisol response in rainbow trout and brown bullhead. BaP exposure also elicited a species-specific transcriptional response at all levelsof the HPI axis.Similarly, the HPI axis response to a standardized emersionstressor revealed species-specific differences. In the field, exposure of different brown bullhead populations to sediment with complex PAH mixtures did not consistently affect cortisol levels and providedno evidence of genetic adaptation of the stress response. Thus, future studies are needed to bridge the gap in our understanding between the laboratory and field effects of PAHs on the stress response of fish.

North American freshwater catfishes (Ictaluridae) is family of freshwater catfishes and includes 7 genera and 48 species. Original habitat of those family is Northern and Central America, but some species were to be introduced to the other regions inclusive Europe. In Czech Republic was recorded occurrence of two species of genus Ameiurus. Brown bullhead (Ameiurus nebulosus) imported by J. Šusta in 1890, and black bullhead (Ameiurus melas), which was imported in 2003 as an admixture to load of Common carp stocking material from Croatia. Distribution of these species is restricted on a small areas in the Elbe river basin and Třeboň pond system in Southern Bohemia. These species are very similar and their resolution is possible only on the basis morphometrics and anatomical diversity (number of fin rays, serration of spine on pectoral fin). Therefore was necessary carry out detailed measuring of both species with the aim of find out appropriate next differences. We measured 63 measurements by digital slide gauge and next we quantified number of fin rays. Totaly was processed 90 black bullheads and 52 brown bullheads.

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Catfish pectoral spines are an anti-predator defense mechanism. They can be bound or locked, making the fish harder to swallow, or used to produce distress calls by rubbing ridges on the dorsal process against a channel in the wall of the pectoral girdle. Growth of the pectoral spine and girdle were examined in relation to fish size within and across species that occur throughout central and eastern Virginia. These included blue catfish (Ictalurus furcatus), channel catfish (Ictalurus punctatus), white catfish (Ameiurus catus), brown bullheads (Ameiurus nebulosus), yellow bullheads (Ameiurus natalis), flathead catfish (Pylodictis olivaris), margined madtom (Noturus insignis), and tadpole madtom (Noturus gyrinus).Pectoral spines and girdles grow as catfish increase in size. In larger species spine length and weight increase nonlinearly with fish size, suggesting that maintaining spine dimensions becomes less important in bigger individuals less likely to suffer predation. The incidence of spine breakage also increases in larger fish. In smaller species spine length increases linearly in our samples (brown and yellow bullheads and margined and tadpole madtoms). In all species spine width increases linearly with total length. The spine base (dorsal process width and depth and dorsal-ventral length) grows linearly with total length in most species. However, measurements of the spine base increase nonlinearly in white catfishes, and dorsal process width increases nonlinearly in wild channel catfish although the increase was linear in cultured channel catfish.Girdle depth increased linearly with total length in all species except for wild channel catfish, and the ratio of coracoid to cleithrum depth varied among species. Pectoral girdle weight increased linearly with fish weight in blue catfish, cultured channel catfish, brown bullheads, and margined and tadpole madtoms. However, girdle weight, a major component of the body, increased nonlinearly in wild channel, white, yellow bullheads, and flathead catfishes. Cultured channel catfish had smaller pectoral spines and girdles than wild channels, a likely epigenetic response to predators. Catfish spines were identified to species, allowing determination of catfishes eaten by bald eagles (Haliaeetus leucocephalus) using spines collected near their nests. Bald eagles ate blue catfish (60%), channel catfish (27%), white catfish (9%), brown bullheads (4%) and yellow bullheads (0.5%). Madtom and flathead catfish were not consumed. Mean sizes captured were: Blue catfish (366 mm, 414 g), channel catfish (417 mm, 618 g), white catfish (320 mm, 591 g), brown bullheads (278 mm, 277 g) and yellow bullhead (203 mm, 192 g).