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This study used microsatellite loci to provide evidence of isolation by distance and an effect of artificial impoundments on the genetic diversity of Channel Catfish Ictalurus punctatus from the Wabash and Ohio rivers. The Wabash River is the longest free-flowing river east of the Mississippi River in the USA, and the Ohio River is highly impounded, yet both rivers support large Channel Catfish fisheries. There was a significant positive relationship between genetic differentiation and geographic distance indicating isolation by distance. Clustering with the programs, STRUCTURE and GENELAND, and principal component analysis revealed multiple genetic clusters, and several sites had results consistent with adults existing as mixtures of genetic groups. These results suggest that the rate of straying among reproductive sites or dispersal is dependent on geographic distance. Channel Catfish from the unimpounded Wabash River had higher genetic diversity (Ho and He) than that from the impounded Ohio Riv...

AQUI-S 20E (10% eugenol) has been shown to be an effective fish sedative for freshwater finfish, but to be approved for use in the United States, the U.S. Food and Drug Administration must be provided with data demonstrating the product is safe to treated animals. Accordingly, we evaluated the safety of AQUI-S 20E when used to sedate Rainbow Trout Oncorhynchus mykiss, Yellow Perch Perca flavescens, and Channel Catfish Ictalurus punctatus. After identifying the highest effective concentrations likely to be used by fisheries biologists to sedate each species to handleable, replicate groups of fish were exposed to this intended concentration (1×) or a 50% higher eugenol concentration (1.5×) for periods of time adequate to effectively sedate 80% of fish to handleable (ET80) or for predetermined treatment periods exceeding the ET80. These predetermined treatment doses (40 and 60 mg eugenol/L for Rainbow Trout, 80 and 120 mg eugenol/L for Yellow Perch, and 100 and 150 mg eugenol/L for Channel Catfish), ...

Nonnative bigheaded carps are established in the Mississippi River and there is substantial concern about their potential entry into the interconnected Laurentian Great Lakes. While electrical barriers currently exist as a preventative measure, there is need for additional control mechanisms to promote barrier security through redundancy. We tested the effectiveness of infused carbon dioxide gas (CO2) as a tool to influence the movement and behavior invasive bigheaded carps, namely Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix, as well as native Bigmouth Buffalo Ictiobus cyprinellus, Channel Catfish Ictalurus punctatus, Paddlefish Polyodon spathula, and Yellow Perch Perca flavescens in an experimental pond. Individuals were monitored with acoustic telemetry before, during, and after CO2 addition to the pond. We noted distinct changes in fish behavior following CO2 addition. Each species except Paddlefish maintained farther distances from the CO2 infusion manifold relative to ...

Species distribution models are useful tools to evaluate habitat relationships of fishes. We used hierarchical Bayesian multispecies mixture models to evaluate the relationships of both detection and abundance with habitat of reservoir fishes caught using tandem hoop nets. A total of 7,212 fish from 12 species were captured, and the majority of the catch was composed of Channel Catfish Ictalurus punctatus (46%), Bluegill Lepomis macrochirus (25%), and White Crappie Pomoxis annularis (14%). Detection estimates ranged from 8% to 69%, and modeling results suggested that fishes were primarily influenced by reservoir size and context, water clarity and temperature, and land-use types. Species were differentially abundant within and among habitat types, and some fishes were found to be more abundant in turbid, less impacted (e.g., by urbanization and agriculture) reservoirs with longer shoreline lengths; whereas, other species were found more often in clear, nutrient-rich impoundments that had generally...

Pugheaded fish exhibit anomalous bone structure, often characterized by a steep, bulging forehead and incomplete closure of the mouth. While the pughead deformity has been observed in many species of fish, thescientific literature contains no documented instances of pugheadedness in Blue Catfish Ictalurus furcatus. Pugheadedness is rare, particularly in tidal systems, and most recorded instances have been based on single specimens. We captured several pugheaded Blue Catfish (N = 18) in the tidal Rappahannock River in eastern Virginia, a tributary of the Chesapeake Bay. While Blue Catfish sampling was extensive in the James, Pamunkey, and Mattaponi rivers (N = 4,357 fish at 163 sites), pugheaded specimens were encountered at only six sampling sites within the upper tidal zone of the Rappahannock River, an area known to be susceptible to summertime hypoxia. We encountered pugheaded individuals at a higher rate than reported in most published studies, ranging between 1.89% and 3.68%, much higher than...

Hydrokinetic energy is proposed as an environmentally preferred means of generating electricity from river and tidal currents. To resolve environmental concerns, it is important to investigate potential effects on aquatic organisms from the electromagnetic fields (EMFs) that are created by underwater generators and transmission cables. We evaluated the behavioral responses of some representative freshwater fishes to static and variable EMFs in a series of laboratory experiments. Fish were exposed for 46 h to a static (DC) EMF with a permanent bar magnet or to a variable (AC) EMF with an electromagnet. Fish locations were recorded with a digital imaging system, and changes in activity level and distribution relative to the magnet position were quantified at 5-min intervals. Experiments with Fathead Minnow Pimephales promelas, Redear Sunfish Lepomis microlophus, Striped Bass Morone saxatilis, Lake Sturgeon Acipenser fulvescens, and Channel Catfish Ictalurus punctatus produced mixed results. Except ...

Using critical thermal maximum (CTMax) tests, we examined the relationship between upper temperature tolerances and fish size (fry–adult or subadult lengths) of rainbow trout Oncorhynchus mykiss (41–200-mm TL), Apache trout O. gilae apache (40–220-mm TL), largemouth bass Micropterus salmoides (72–266-mm TL), Nile tilapia Oreochromis niloticus (35–206-mm TL), channel catfish Ictalurus punctatus (62–264 mm-TL), and Rio Grande cutthroat trout O. clarkii virginalis (36–181-mm TL). Rainbow trout and Apache trout were acclimated at 18°C, Rio Grande cutthroat trout were acclimated at 14°C, and Nile tilapia, largemouth bass, and channel catfish were acclimated at 25°C, all for 14 d. Critical thermal maximum temperatures were estimated and data were analyzed using simple linear regression. There was no significant relationship (P > 0.05) between thermal tolerance and length for Nile tilapia (P = 0.33), channel catfish (P = 0.55), rainbow trout (P = 0.76), or largemouth bass (P = 0.93) for the length range...

Collections of 231 catfish from 34 localities were surveyed for mtDNA (399 base pairs of cytochrome b) and morphological evidence of headwater catfish Ictalurus lupus in areas of historical occurrence in Texas and New Mexico. The species is of concern for conservation managers, primarily because of the potential for population losses from competition and hybridization with channel catfish I. punctatus. For cytochrome b, there were two deeply divergent (4.8–6.1%) groups, a channel catfish clade of 14 haplotypes (0.8% to 1.3% divergence) and a headwater catfish clade of two haplotypes (1.0% divergence), associated with morphotypes of channel catfish and headwater catfish, respectively. Morphotypes were based on field identification and a canonical discriminant function utilizing external morphology. All specimens from the Nueces River and the main-stem Rio Grande and the Pecos River conformed to morphological and mtDNA expectations for channel catfish. Apparently pure populations of headwater catfi...

Channel catfish Ictalurus punctatus are commonly stocked into small impoundments and may become abundant in these waters. When channel catfish are abundant, they may compete with bluegills Lepomis macrochirus for macroinvertebrate prey, resulting in reduced growth and size structure of bluegills. I determined whether bluegill growth and size structure were related to the varying abundance of channel catfish by means of two experimental pond studies and small-lake survey data. In the first pond experiment, 16 ponds were stocked with bluegills at 39.5 kg/ha and with channel catfish at a rate of 10, 30, 50, or 100 kg/ha (4 ponds/treatment). In the second pond experiment, 12 ponds were stocked with one of four bluegill–channel catfish biomass combinations (3 ponds/treatment): 15 and 70 kg/ha, 15 and 130 kg/ha, 70 and 70 kg/ha, or 70 and 130 kg/ha. Bluegill growth increments (both length and mass) did not decrease with increases in channel catfish biomass in either experiment, but both fish species ex...

We investigated basin-scale factors that were likely to influence the growth of channel catfish Ictalurus punctatus in Mississippi floodplain rivers. Channel catfish were collected from nine streams during 2001–2002. All fish were measured (total length; mm) and aged from pectoral spine sections. Linear growth models were fitted to mean back-calculated length-at-age data for channel catfish from each stream and were compared among streams. Channel catfish growth rate differed among streams. Multiple linear regression was used to correlate growth rate to basin-scale environmental variables. The growth rate for channel catfish was related positively to soil fertility and negatively to altitude and percentage of the watershed comprising bottomland hardwood forest. Basin-scale determination of environmental features related to channel catfish growth can assist managers and fisheries administrators with establishment of realistic expectations for riverine channel catfish fisheries at a scale that is a...

Ten species of fish were exposed to homogeneous electric fields of 60-Hz pulsed DC in water having an ambient conductivity of 100 μS/cm. A range of voltage gradients was used for the electroshock, and the percentage of fish dead after 1 h was determined. A logistic model was used to compare species, and the voltage gradient that was lethal within 1 h to 50% of the fish (LV50) was computed. Except for blackbanded darters Percina nigrofasciata (juveniles and adults) and western mosquitofish Gambusia affinis (adults), all fish were newly transformed juveniles, which for some species are more sensitive to the lethal effects of electroshock than are younger or older fish. The most susceptible species was the blackbanded darter (LV50 = 1.7 V/ cm), followed by largemouth bass Micropterus salmoides (LV50 = 3.0 V/cm), striped bass Morone saxatilis (LV50 = 4.0 V/cm), and channel catfish Ictalurus punctatus (LV50 = 4.1 V/cm). Species of intermediate susceptibility were the rainbow trout Oncorhynchus mykiss ...

Slat traps are a passive gear used in freshwaters of the southeastern United States, primarily for catfishes (family Ictaluridae) in commercial fisheries. They are particularly selective for channel catfish Ictalurus punctatus. Slat traps have four interslat spaces of defined width that are designed to allow undersized individuals to escape. We conducted two experiments to assess the relationship between the width of the interslat spaces and the length of the channel catfish retained in the trap. Slat traps having interslat spaces of 1 and 2 cm retained all fish larger than 250 mm. Increasing the width of the interslat spaces from 2 cm to 3, 3.8, and 5 cm resulted in the escape of progressively larger fish from the trap. Traps having interslat spaces of more than 5 cm retained no channel catfish. Size selectivity did not differ between traps with 1-cm and 3-cm interslat spaces for channel catfish larger than 250 mm. The 3.8-cm trap selected for larger fish and showed a 50% probability of retainin...

Immediate mortality of electroshocked fish was related to the stage of development after hatching. Larvae and juveniles of four species of fish were exposed to homogeneous voltage gradients (2–16 V/cm) of 60-Hz pulsed DC in water having an ambient conductivity of 100 μS/cm. Recently hatched fish and fish older than 100 d did not die after electroshocking. The developmental period most susceptible to electroshocking-induced mortality was near the time of transformation from larvae to juveniles for all four species. The highest predicted mortality occurred 22 d after hatching or at 19–21 mm total length (TL) for bluegill Lepomis macrochirus, 36–41 d or 29–32 mm TL for largemouth bass Micropterus salmoides, 42–43 d or 27–30 mm TL for channel catfish Ictalurus punctatus, and 38 d or 21 mm TL for Nile tilapia Oreochromis niloticus. During a 5-d observation period, there was no delayed mortality of channel catfish. A field validation experiment with 25-d-old largemouth bass (14–22 mm TL) indicated that...

Reproductive traits of the channel catfish Ictalurus punctatus, the blue catfish I. furcatus, their F1 hybrid—channel catfish female × blue catfish male—and their F2 hybrid were examined. The absence of reproductive isolating mechanisms in F1 and F2 generations is important in terms of allowing for breeding programs for the development of a synthetic breed that has the best culture traits from the two species. Conversely, if reproductive fitness is high in F1 and F2 generations, the possibility of introgression with the parent species in the natural environment increases, thereby increasing the potential for risk from F1 generation (and higher) hybrids. F2 hybrid females had a lower frequency of ovulation (P < 0.05; 12.2%) than did channel catfish, blue catfish, and F1 hybrid catfish (83.5, 58.4, and 56.5%, respectively) when these females were induced to spawn with carp pituitary extract and were then hand-stripped. F2 hybrids that ovulated produced fewer eggs per kilogram of body weight (P < 0....

During early life stages, fish in the Mississippi River system may become stranded by shoreline drawdowns induced by the passage of commercial vessels. We examined the stranding of larval shovelnose sturgeon Scaphirhynchus platorynchus, paddlefish Polyodon spathula, and bigmouth buffalo Ictiobus cyprinellus and of juvenile blue catfish Ictalurus furcatus, largemouth bass Micropterus salmoides, and bluegill Lepomis macrochirus in a laboratory flume. Stranding was measured at three vertical drawdown rates (0.76, 0.46, and 0.21 cm/s) and two bank slopes (1:5 and 1:10). Blue catfish, shovelnose sturgeon, and paddlefish were not tested at both bank slopes. Susceptibility to stranding varied among species and was independent of drawdown rate. At a slope of 1:5, shovelnose sturgeons had the highest stranding percentage (66.7%), followed by paddlefish (38.0%), bluegills (20.0%), bigmouth buffalo (2.2%), and largemouth bass (0.0%). At 1:10, blue catfish had the highest stranding percentage (26.7%), follow...

Transintestinal expulsion of surgical implants by fish is an exceptional phenomenon, except in the case of channel catfish Ictalurus punctatus. In order to test whether this mechanism was shared by other siluriform species, passive integrated transponder tags and epoxy dummy transmitters (0.5–2.0% of fish body weight) were surgically implanted into the peritoneal cavity of age-0, age-1, and age-2 African catfish Heterobranchus longifilis, which are known as vundu or sampa, (20 fish in each group). Transmitters were placed posterior to midventral incisions, which were closed with braided silk or polyamide stitches. Four tags were expelled through the incision within 4 d, and six others were expelled through the intestine from day 8 to day 12. Necropsies of sampled fish retaining their tag until day 14 indicated six additional situations that were indications of potential expulsion through the intestine (N = 5) or body wall (N = 1). No other tag was expelled later than day 14, and final necropsies ...

Genomic research requires many molecular markers for construction of the genetic linkage map and for marker-assisted selection (MAS). Amplified fragment length polymorphism (AFLP) markers are inherited with Mendelian expectations in catfish and, thus, are suitable for use in gene mapping and MAS. To identify large numbers of AFLP markers, 64 primer combinations were tested to generate AFLP patterns between channel catfish Ictalurus punctatus and blue catfish I. furcatus. The 64 primer combinations amplified 7,871 bands, of which 3,081 were polymorphic between the two mating parents of channel catfish and blue catfish used to produce the reference families for mapping analysis. The primer combinations that produced fewer bands showed higher rates of polymorphism. Of the 64 primers, 53 primer combinations produced clean and reproducible AFLP profiles. Nine primer combinations produced fair AFLP profiles. The remaining two primers produced poor AFLP profiles with intensive background bands. The 53 e...

Thermal acclimation dynamics of channel catfish Ictalurus punctatus were quantified by using time-series critical thermal maximum (CTMax) estimates. Data consisted of CTMax determinations from 57 groups of 10 fish each. Respective CTMax values ranged from 30.9°C to 42.1°C for acclimation temperatures between 10°C and 35°C and increased 0.45°C for each 1°C increase in acclimation temperature. Rates of heat tolerance gain for fish transferred from low to high temperatures were not constant but decreased geometrically with respect to time until end-acclimation levels were reached. Fish transferred from high to low temperatures showed similar geometric patterns of tolerance loss; however, progressive decrease in CTMax was relatively slow and was interrupted after 24 h by a consistent 72-h acclimatory stasis. Differential patterns of heat tolerance gain and loss suggest that both processes place a premium on heat tolerance conservation. Acclimation times were influenced directly by absolute difference...

Successful cryopreservation of fish spermatozoa has important implications for genomic conservation and for aquaculture. We report the first long-term cryopreservation of ictalurid sperm. Spermatozoa from nine blue catfish Ictalurus furcatus were cryopreserved for 12 months in three concentrations (3.75 × 108, 1.50 × 109, and 6.00 × 109 spermatozoa per straw), within two different straw sizes (0.5 and 1.0 mL), and with two cryoprotectants (DMSO or methanol combined with powdered skim milk). Cryopreserved spermatozoa were then used to fertilize lots of 450 eggs of channel catfish Ictalurus punctatus. Mean relative fertilization percentage for sperm treated with DMSO was 32% (range of 23–54%) of the fresh control. Spermatozoa frozen with the combination of an intracellular cryoprotectant (methanol) and an extracellular cryoprotectant (skim milk) produced no fertilization. No difference (P > 0.05) was observed between fertilization percentage of spermatozoa frozen in the two straw sizes. The highest...

Artificial spawning of channel catfish Ictalurus punctatus relies on the removal of testis and suspension of sperm in an extender solution for storage and use in fertilization. Little is known about the relationships among osmotic pressure, sperm activation, motility, and storage. Our objectives were to (1) estimate motility of channel catfish sperm diluted in solutions ranging in osmotic pressure from 8 to 295 milliosmols (mosmol)/kg, (2) identify the osmotic pressure that induces threshold activation (10% motility) and the highest pressure that induces complete activation, (3) determine the role of ionic dilution in activation by use of ion-deficient solutions, and (4) evaluate the effect of osmotic pressure on the retention of motility during storage. Motility (percentage of actively swimming sperm) was estimated in diluted Hanks' balanced salt solution (HBSS) and sucrose solutions over a range of osmotic pressures. The HBSS osmotic pressures of threshold and complete activation were 218 ± 15 ...

We examined relationships between lower Mississippi River physicochemistry and growth of young (≤age 2) blue catfish Ictalurus furcatus, channel catfish I. punctatus, freshwater drum Aplodinotus grunniens, and gizzard shad Dorosoma cepedianum collected from dike fields (river kilometers 669.0–883.2 upstream from the mouth) in September and October 1987–1990. Growth increments of the four fishes were determined from cross sections of otoliths (freshwater drum and gizzard shad) or spines (blue and channel catfishes), and we used regression analysis to assess the effects of annual variability in 15 physicochemical variables on growth. We hypothesized that growth of these fishes would be positively related to the extent and duration of the annual flood pulse, as it is in tropical floodplain systems. However, growth increments of age-0 blue catfish, channel catfish, and gizzard shad were related only to length of the growing season. Further, positive relationships between growth and total organic carb...

The purpose of this study was to compare external morphological variation between the headwater catfish Ictalurus lupus and the channel catfish Ictalurus punctatus, and to determine if external characters could be used to improve our ability to identify these highly similar species, as most individuals cannot be identified in the field using available methods. Morphological differences were found between species but were obscured by geographic variation and allometric growth. Overall, headwater catfish tended to be broader, have shorter spines, and have a shorter anal fin base than channel catfish when measurements were adjusted for body size. Fish of both species were broader in New Mexico than their counterparts in Texas; headwater catfish from Mexico tended to be intermediate. A south-to-north cline of decreasing anal ray counts was observed for both species. Each species exhibited similar patterns of allometric growth, with snout and mouth widths and interorbital distances increasing, and len...

We evaluated two methods, boiling and microwave irradiation, for the rapid isolation of DNA from barbel, adipose fin, and blood of channel catfish Ictalurus punctatus. Compared with routine DNA isolation methods, these procedures were fast (microwaving, 2–4 min; boiling, 10–18 min), simple, and inexpensive (about US$0.10/fish). Samples of DNA isolated from barbels of small (mean ± SD, 2.9 ± 1.0 g) and large (290 ± 43 g) fish were of high purity (ratios of absorbances at 260 and 280 nm, A260/A280 = 1.72–1.90) and were between 0.29 and 0.67 μg/μL in concentration. Samples of DNA isolated from barbel, adipose fin, and blood of small fish, by either method, were used successfully for analysis by polymerase chain reaction (PCR). Samples isolated by boiling of barbel and blood from large fish also proved useful for PCR analysis. These DNA isolation procedures would be useful for rapid genetic screening of channel catfish. Removal of the barbel for tissue analysis would also enable direct marking of fis...

Cross sections of pectoral spines were used to identify hatchery-reared and wild channel catfish Ictalurus punctatus in the Buffalo River, Arkansas. Stocked, catchable-size catfish could be identified by wide growth increments between the first and second annuli (corresponding to rapid hatchery growth) followed by narrow annual increments beyond age 2 (corresponding to slower posthatchery growth). For stocked fish, the mean width between the first and second annulus of the spine section was 3.4 times wider than the mean width between the second and third annulus. In wild fish these widths were not significantly different. This growth pattern for stocked fish was verified by using pectoral spines obtained from marked hatchery fish stocked in 1990 and 1991, and by comparing back-calculated lengths of suspected hatchery fish at age 2 with the length at stocking. By the use of this method, it was determined that previously stocked catfish accounted for more than 92% of the catfish sampled in the Buff...

Studies were conducted to address glucuronidation of 3-trifluoromethyl-4-nitrophenol (TFM) in sea lampreys Petromyzon marinus, channel catfish Ictalurus punctatus, rainbow trout Oncorhynchus mykiss, and bluegills Lepomis macrochirus. The ability of these species to biotransform TFM was investigated by determining the kinetics of UDP-glucuronyltransferase (UDPGT; also known as glucuronosyltransferase) in vitro from hepatic microsomal preparations. Maximal velocity (V max, nmol/min·mg) for UDPGT activity toward TFM was significantly greater (P rainbow trout (97 μM) > channel catfish (172 μM) > sea lamprey (261 μM). Analysis of V max/K m ratios, a measure of enzyme efficiency (nmol/min-mguM TFM), indicated that the efficiency of UDPGT activities in all species examined was in...

Polymorphic isozymes visualized by starch gel electrophoresis and histochemical staining were examined in parents and 1,000 progeny of 24 single-pair matings of channel catfish Ictalurus punctatus and three interspecific crosses of channel catfish × blue catfish I. furcatus. Polymorphic loci that could be scored from fin tissue included aconitate hydratase (mAH*), glucose-6-phosphate isomerase (GPI-B*), glutathione reductase (GR*), phosphoglucomutase (PGM*), and UDPglucose-hexose-1-phosphate uridylyltransferase (UGHUT-2*). Inheritance of observed electrophoretic variation was consistent with Mendelian segregation of codominant alleles in progeny selected randomly from the individual crosses. Although mAH*, GPI-B*, PGM*, and UGHUT-2* appeared to assort independently within the limits of the data, strong evidence for linkage of GR* and PGM* was obtained (19.7% recombination, P ≤ 0.001 for data combined from two informative pedigrees); this linkage was designated Ictalurus punctatus linkage group I....

Electrophoretic analysis of enzymes and proteins enables aquaculturists to distinguish among stocks of channel catfish Ictalurus punctatus and blue catfish I. furcatus, and to monitor gene flow, hybridization, and inbreeding. Sixteen previously unreported genetic markers allow much more precise resolution of stock differences. Analysis of low-risk tissue samples (caudal fin, adipose fin, and barbels) enables investigators to obtain genetic data with little stress on individual fish. We have identified at least 69 enzyme locus products in populations of channel catfish (Kansas, Marion, “Auburn,” Mississippi, and Red River strains) and blue catfish by use of autopsied tissues. Polymorphic loci account for at least 36% of the loci examined. Allelic polymorphisms fixed between blue and channel catfish were observed at 13 loci. Genetic variation was observed at 17 loci among channel catfish populations and at 5 loci in the single blue catfish population. Analysis of species-specific genetic markers am...

Adult northern squawfish Ptychocheilus oregonensis, walleyes Stizostedion vitreum, smallmouth bass Micropterus dolomieu, and channel catfish Ictalurus punctatus were sampled from four regions of John Day Reservoir from April to August 1983–1986 to quantify their consumption of 13 species of prey fish, particularly seaward-migrating juvenile Pacific salmon and steelhead (Oncorhynchus spp.). Consumption rates were estimated from field data on stomach contents and digestion rate relations determined in previous investigations. For each predator, consumption rates varied by reservoir area, month, time of day, and predator size or age. The greatest daily consumption of salmonids by northern squawfish and channel catfish (0.7 and 0.5 prey/predator) occurred in the upper end of the reservoir below McNary Dam. Greatest daily predation by walleyes (0.2 prey/predator) and smallmouth bass (0.04) occurred in the middle and lower reservoir. Consumption rates of all predators were highest in July, concurrent w...

Diets of northern squawfish Ptychocheilus oregonensis, smallmouth bass Micropterus dolomieu, walleye Stizostedion vitreum, and channel catfish Ictalurus punctatus from John Day Reservoir were examined to determine the extent of predation on juvenile salmonids during seaward migrations of the salmonids during April–August 1983–1986. Juvenile Pacific salmon Oncorhynchus spp. and steelhead O. mykiss were the most important food group (by weight) of northern squawfish – about 67% – but made up smaller proportions of the food of the other predators: channel catfish, 33%; walleyes, 14%; smallmouth bass, 4%. Seasonal changes in diets indicated that northern squawfish preferred juvenile salmonids in May and August (generally the peak period of salmonid out-migration), and switched to prickly sculpin Cottus asper when numbers of juvenile salmonids declined; walleyes and smallmouth bass showed a preference only for prickly sculpin among the prey fishes analyzed. As judged by dietary composition and prey se...

Channel catfish Ictalurus punctatus were reared for 2 years on practical feeds with and without a topdressing of oil (50% animal, 50% vegetable). Visceral fat, fillet fat, and whole-body protein increased and moisture percentage decreased as fish size and age increased. Slopes of regression lines for these variables differed significantly between treatments. Fatty acid profiles of fillets showed essentially linear trends toward decreasing saturation and increasing unsaturation with increasing size and age of fish. Within the unsaturated fatty acids, monene levels increased, and diene and triene levels decreased. Topdressing with oil did not affect these trends. Although dietary lipid composition is a major influence on fatty acid composition in channel catfish, this study indicates that fish size and age also significantly influence fatty acid profiles.

We report the rare, natural occurrence of triploidy in a brown bullhead Ameiurus (formerly Ictalurus) nebulosus. This is to our knowledge the first report of naturally occurring triploidy within the family Ictaluridae. The nuclei of blood cells were studied by flow cytometry, volume measurement, and computer-assisted image analysis. The triploid had a genome size of 3.29 pg DNA/cell compared to 2.23 pg DNA/cell (SD, 0.02 pg) for 28 diploid brown bullheads. Volume measurement and image analysis were able to detect the triploid condition; however, flow cytometry was the most precise technique and had the greatest resolution.

Cooling water for a 220-megawatt power plant is pumped from 5 m beneath Lake Monona's surface, heated about 10 C, and discharged into the littoral zone. Maximum temperatures in the effluent-outfall area approach 35 C in summer and 14 C in winter; unheated parts of the littoral zone rarely exceed 29 C. To assess distributional responses of fishes to operation of the power plant, the outfall area and two reference areas were electrofished on 30 dates between 8 August 1968 and 21 August 1969. Some fishes avoided the outfall area; these were Perca flavescens, Cottus bairdi, subadult Morone mississippiensis, and subadult Ictalurus melas. Others were occasionally or usually concentrated in the outfall area relative to reference areas—Lepisosteus osseus, adult Cyprinus carpio, adult M. mississippiensis, young Lepomis gibbosus, L. macrochirus, and Micropterus salmoides. The tendency for fish of a given species and size to concentrate in or avoid the outfall area generally did not reverse from season to s...

Standing stocks (kg/hectare) of channel catfish Ictalurus punctatus were graphed against 19 abiotic variables measured for Kansas streams. The resulting habitat suitability curve for each variable allowed fish biomass to be normalized to index values (range, 0.0–1.0) that could be regressed linearly against the abiotic variables. Stepwise multiple-regression techniques isolated three variables (runoff, fraction of stream area consisting of runs, and water temperature) that accounted for nearly half the variability in channel catfish biomass. When the regression model derived from Kansas data was applied to an independent data set from Oklahoma, the correlation between predicted and observed standing stocks was highly significant, though low. Assigning suitability index values to the Oklahoma data set from the habitat suitability curves developed from Kansas data resulted in a significant model with more (often different) variables accounting for three-fourths of the biomass variability. The regre...

The morphology, dimensions, aberrations, and ultrastructure of channel catfish (Ictalurus punctatus) spermatozoa were studied. Spermatozoa of a wild catfish stock from Louisiana were compared to those of a domestic stock from Mississippi. The spermatozoon of channel catfish consists of a rounded dark head, a collar-dike midpiece, and a long flagellum. The average dimensions were: head length, 2.3 μm; midpiece length, 1.6 μm; midpiece width, 3.1 μm; and flagellum length, 94.9 μm. The flagellum had the classical (2.9 + 2) axoneme. On the average, 4.7% of the spermatozoa in the fish studied were biflagellar. Each flagellum arose from an individual centriolar complex. Domestic fish stock had a higher percentage of normal gametes compared to wild stock.

Channel catfish (Ictalurus punctatus) were stocked in 0.02 to 0.04-hectare ponds without aeration at three rates (4,942, 10,007, and 20,385 fish per hectare) and fed daily. Fish averaged 12 cm total length and 10 g at stocking. Each treatment was replicated six times. Maximum feeding rates of 34, 56, and 78 kg/hectare, respectively, were reached by midsummer. In the low treatment, no dissolved oxygen (DO) problems occurred, and survival was 99%. In the medium treatment, DO at dawn frequently fell below 2.0 mg/liter and some fish suffocated during an oxygen depletion in one pond; however, survival averaged 93%. In the high treatment, DO at dawn was usually below 2.0 mg/liter in August and September. Fish mortalities resulted from DO depletion in three ponds of the high treatment, but survival averaged 83%. Nitrite-nitrogen and un-ionized ammonia never reached concentrations recognized to be lethal to channel catfish in any of the treatments. However, concentrations of un-ionized ammonia were possi...

Eight static 24-h median lethal tests were conducted with 16-g channel catfish Ictalurus punctatus at water temperatures of about 21°C. Tests were performed at four acidities with ammonium chloride and with ammonium sulfate. When compared on the basis of un-ionized ammonia nitrogen (NH3-N), ammonium chloride solutions were more toxic than ammonium sulfate solutions. Median lethal concentrations (24-h LC50s) at pH 8.8, 8.0, 7.2, and 6.0 were, respectively, 1.91, 1.45, 1.04, and 0.74 mg NH3-N/L for ammonium chloride, and 2.24, 1.75, 1.16, and 0.81 mg NH3-N/L for ammonium sulfate. Ionized ammonia (NH 4) was not lethal at concentrations up to 1,787 mg NH 4-N/L. Slopes of the probit regressions of NH3-N concentration versus mortality increased with decreases in pH and were nearly vertical at pH 6.0. Hematocrits of channel catfish exposed to lethal ammonia solutions also increased with decreases in pH, indicating an effect on osmoregulation. Plasma osmolality and red blood cell diameters did not change...

Channel catfish (Ictalurus punctatus) were grown from fingerlings to harvestable size in earthen ponds at densities of 197 and 394 fish per 400-m2 pond (49 and 98 per 100 m2) and 494 fish per 200-m2 pen (247 per 100 m2) by intensive feeding of diets with or without supplemental vitamin C. The fish did not require vitamin C in their diets for normal growth or to prevent gross signs of the broken back syndrome at the two lower densities; however, at the highest density growth was 28% less while 23% of the fish showed external signs of the broken back syndrome. Percentages of collagen in bone and vitamin C in liver were statistically lower (P < 0.05) in fish fed the diet deficient in vitamin C. Serum alkaline phosphatase activity, blood hematocrit, and anterior kidney vitamin C level were not influenced by the diets. Feed processing losses of vitamin C were 18 to 27% and 46 to 62% for pelleting and extrusion, respectively. The half-life of vitamin C in stored catfish feeds was 2.6 to 2.9 months.

Channel catfish (Ictalurus punctatus) were stocked in 0.02- and 0.04-hectare ponds at 20,385 fish per hectare and fed daily. Fish averaged 11 cm total length and 6.2 g at stocking. Six ponds received nightly aeration (2 to 6 hours) and six ponds received no aeration. A maximum feeding rate of 90 kg/hectare was reached in October. In aerated ponds, no dissolved oxygen (DO) problems occurred, and survival was 92%. Fish mortalities resulted from DO depletion in all unaerated ponds, and survival was 40%. Nitrite-nitrogen concentrations were significantly higher in the aerated ponds, though never at levels reported as lethal to channel catfish. Concentrations of un-ionized ammonia were high enough in both aerated and unaerated ponds to have adversely affected growth. Aerated ponds yielded an average of 5,307 kg/hectare of channel catfish and had a net economic gain of $1,500 per hectare. The unaerated ponds yielded an average of 1,400 kg/hectare and were an obvious economic failure. Direct extrapolati...

Two wild and two domestic strains of channel catfish Ictalurus punctatus demonstrated different spawning periods among strains. This character may be under genetic control. Egg hatchability was variable and did not differ significantly among strains or strain crosses. Deformed fry occurred in all spawns, but (with one exception) their frequency did not differ significantly among strains or crosses, and may have been due to environmental factors. Female broodfish weight was positively correlated with total weight and number of eggs of the spawn, but negatively correlated with average egg weight. Egg size was not correlated with hatchability or percent deformed fry.

Animals usually encapsulate artificial implants placed in the abdominal cavity, but some fish species are unique in exhibiting transintestinal expulsion of the implant. Gross and histological examination were used to study the mechanisms of expulsion of artificial implants from channel catfish Ictalurus punctatus. Silicone-rubber- or paraffin-coated polystyrene transmitter capsules (0.5% or 2.0% of the fish's body weight) were surgically implanted into the peritoneal cavity of 74 adult channel catfish. Within 23 d, 39 transmitters had been expelled: 14 through the intestine, 24 through the incision, and one through a lesion in the ventral body wall. Two fish died, but 33 fish retained transmitters for the duration of the experiments (14–23 d); at necropsy, four transmitters were free in the abdominal cavity, 11 had limited fibrous proliferation, 14 were fully encapsulated by fibrous connective tissue, and four were partly or fully in the intestinal lumen. A fibrous connective tissue capsule was p...

The effects of the extracellular products (ECP) and endotoxin from Aeromonas hydrophila grown in a defined medium were determined following intraperitoneal injection of young-of-the-year channel catfish Ictalurus punctatus. Endotoxin had no lethal effects in doses as high as 400 μg per 7.2-g fish, whereas ECP had a 48-hour median lethal concentration (LD50) of 15.7 μg per 7.2-g fish. Sublethal doses of ECP often produced many of the gross pathologies associated with A. hydrophila infections. The primary lethal factor was heat-labile at 56 C for 10 minutes, but a heat-stable component was also implicated.

Peripheral blood leucocytes of channel catfish Ictalurus punctatus were characterized by Wright's stain, differential cytochemical stains, and immunofluorescence; lymphocytes, thrombocytes, neutrophils, and monocytes were identified. The morphologically similar neutrophils and monocytes were distinguished with a Sudan black B stain for neutrophils and an assay of nonspecific esterase activity for monocytes. Monocytes also phagocytized polystyrene beads. Leucocytes were physically separated by cytofluorography based upon their forward and 90° light-scattering properties. One population of sorted cells contained almost exclusively lymphocytes, a second contained predominantly thrombocytes, and the third contained both neutrophils and monocytes. Multiparameter cytofluorography with mouse monoclonal antibodies to channel catfish immunoglobulin revealed that a vast majority of leucocytes exhibiting surface immunofluorescence were lymphocytes, though only about 40% of the lymphocytes contained demonstr...

Several experiments were conducted on relationships between oxygen consumption of channel catfish (Ictalurus punctatus) and environmental dissolved oxygen concentrations, feeding status, weight of fish, and temperature. Estimates of oxygen consumption under culture conditions were obtained by determining the rate of oxygen depletion in a still tank without aeration. Respiratory dependence (decrease in oxygen consumption rate with a decrease in environmental oxygen concentration) in both well-fed and fasted fish was noted at oxygen concentrations between 1 and 7 milligrams/liter. The oxygen consumption rates obtained one hour after feeding were higher than those taken immediately after feeding or from fasted fish. A log-log relationship between oxygen consumption and body weight of fish (2.3-1,006 g) was demonstrated. The slope (b) for the equation, oxygen consumption = (a) (weight)b was 0.80 for both well-fed and fasted fish. The relationship between oxygen consumption and environmental temperatu...

The involvement of vitamin C as a cofactor in detoxication mechanisms of fish was investigated by feeding selected amounts of the vitamin in diets of fingerling channel catfish (Ictalurus punctatus) that were concurrently exposed to toxaphene, a widely used organochlorine insecticide in the Southeastern United States. Three groups of fish were exposed continuously to each of five toxaphene concentrations—37, 68, 106, 218, and 475 ng/liter—and fed a diet containing 63, 670, or 5,000 mg/kg of vitamin C. After 150 days of toxaphene exposure, backbone collagen was significantly decreased in most fish fed the diet containing 63 mg/kg of vitamin C. However, the toxaphene concentrations of 37 and 68 ng/liter did not cause this effect in fish fed the 670 mg/kg vitamin C diet, and only the 475 ng/liter concentration significantly depressed backbone collagen in fish fed the 5,000 mg/kg diet. Spinal deformities were common among fish fed low vitamin C diets, but the incidence decreased as dietary vitamin C ...

Basal concentrations of plasma cortisol (near 50 ng/ml) and plasma glucose (near 0.50 mg/ml) were significantly greater in yearling channel catfish (Ictalurus punctatus) acclimated to 10 C than in fish adapted to 20 or 30 C; the latter groups had similar basal levels of cortisol (near 25 ng/ml) and glucose (near 0.30 mg/ml). Fish at 10 C had a slower and less marked increase in cortisol and glucose over minutes, hours, and days in response to the stress of severe confinement than fish at 20 or 30 C which were again similar. No mortality occurred in the fish stressed at 10 C during 3 days of confinement, while 89% died in the 20 C group by day 3 and all fish at 30 C were dead by day 2. Glucose concentrations initially rose more slowly than those of cortisol, but continued to increase between 3 and 12 hours after confinement. Also, glucose returned to near basal levels in dying fish while cortisol was at its highest then. Channel catfish, even at warm temperatures, have a slower and less extensive ...

One hundred sixty-three fish from four natural ponds in Florida were examined for parasites. Of these, 40 were grass carp (Ctenopharyngodon idella), an exotic herbivorous fish which had been introduced for research as a possible biological control of aquatic vegetation. The remaining 123 fish included six native species (largemouth bass, Micropterus salmoides; bluegill, Lepomis macrochirus; golden shiner, Notemigonus crysoleucas; lake chubsucker, Erimyzon sucetta; brown bullhead, Ictalurus nebulosus; yellow bullhead, Ictalurus natalis). Parasite faunas of the native fishes and grass carp were compared. Identified were 37 species of parasites from the native fishes and one species from grass carp. No exotic parasites were observed in the grass carp, but the grass carp were infected by a native parasite of the phylum Pentastomida, Sebekia oxycephala.

Toxicity tests showed that aquatic invertebrates and fish have a broad range of sensitivities to Imidan, an organophosphate insecticide applied agriculturally and possibly to forests. Invertebrate 48-h EC50's (concentration immobilizing 50% of the test organisms) or LC50's (concentration lethal to 50% of the test organisms) ranged from 2.4 μg/liter for amphipods (Gammarus pseudolimnaeus) to 3,200 μg/liter for larval midges (Chironomus plumosus). Among fish tested, chinook salmon (Onchorhynchus tshawytscha) and smallmouth bass (Micropterus dolomieui) were the most sensitive (96-h LC50, 150 μg/liter) and channel catfish (Ictalurus punctatus) the most resistant (96-h LC50, 11,000 μg/liter). Toxicities of the active ingredient to fishes were similar for the technical grade Imidan and the 50% wettable powder formulation. Toxicities to fish increased with the increasing temperature and decreasing pH, but were unaffected by water hardness. Eyed eggs and yolk-sac fry of rainbow trout (Salmo gairdneri) we...

Channel catfish Ictalurus punctatus subjected to a diet deficient in vitamin C for 150 days showed a decrease in backbone collagen and hydroxyproline concentrations, whereas the mineral: Collagen ratio and bone density increased. These changes resulted in a 20% reduction in bone strength and a 46% increase in vertebral elasticity. The backbone of channel catfish exposed to the insecticide toxaphene for 90 days also had decreased collagen, but hydroxyproline concentration, mineral: Collagen ratio, and bone density all increased. These alterations in backbone composition resulted in a 34% increase in strength and a 39% decrease in vertebral elasticity. In both experiments, hydroxyproline concentrations in backbone collagen had the greatest influence on the structural properties of vertebrae, whereas collagen, calcium, and phosphorus concentrations did not. Mechanical properties seemed to be more sensitive indicators of vertebral structural integrity than did biochemical ones or bone density.

The 96-h LC50's for potassium permanganate (KMnO4) ranged from 0.750 mg/liter with channel catfish, Ictalurus punctatus, to 3.60 mg/liter with goldfish, Carassius auratus, in laboratory tests. The toxicity of KMnO4 to fish is greatest in water of lower temperatures, in harder water, or in higher pH water. KMnO4 is effective for detoxifying the fish toxicant antimycin in laboratory waters of pH 6.5 to 9.5. The half-life for antimycin exposed to 1.0 mg/liter of KMnO4 ranges from 7 to 11 minutes in the different pH waters at 12 C.

Ten riverine fish species were tested at 10, 20, and 30 C to determine their resistance to monochloramine. The exposure regime consisted of four 40-minute exposures administered at 5-hour intervals over 24 hours. All species exhibited an inverse relationship between temperature and median lethal (LC50) concentrations. LC50 values generally decreased by a factor of two as the exposure temperature increased from 10 to 30 C. LC50 values ranged from 0.35 mg/liter at 30 C for the emerald shiner to 3.00 mg/liter at 10 C for the bluegill. Based on their resistance to monchloramine at 30 C the fish were separated into sensitive and resistant groups. The sensitive group, which included (in decreasing order of sensitivity) the emerald shiner (Notropis atherinoides), spotfin shiner (Notropis spilopterus), common shiner (Notropis cornutus), channel catfish (Ictalurus punctatus), white sucker (Catastomus commersoni), and sauger (Stizostedion canadense), had LC50 values ranging from 0.35 to 0.71 mg/liter. The ...