We compared growth of flathead catfish Pylodictis olivaris from two native populations in Alabama (Coosa and Tallapoosa rivers) and two introduced populations in Georgia (Ocmulgee and Satilla rivers). We also compared mortality rates and potential outcomes of various management regimes (minimum length limits [MLLs]) among the populations. Total length–log10(age) regression slopes for introduced fish were higher than those for native fish, and von Bertalanffy growth coefficients (K) were greater for introduced fish (Ocmulgee: 0.195; Satilla: 0.201) than for native individuals (Coosa: 0.057; Tallapoosa: 0.059). Therefore, introduced flathead catfish grew more rapidly than those in their native range. Mortality (instantaneous mortality rate, Z) was higher in the Satilla River population (Z = −0.602) than in the Ocmulgee River (Z = −0.227) and Coosa River (Z = −0.156) populations. However, fish in the Satilla River population had been introduced for only 10 years and presumably did not reach their theoretical maximum age, potentially biasing the mortality estimate for that population. Simulation of management regimes in Fishery Analyses and Simulation Tools software predicted that maximum biomass of flathead catfish in the Ocmulgee (1,668 kg) and Satilla (1,137 kg) rivers was substantially larger than that in the Coosa (873 kg) and Tallapoosa (768 kg) populations. However, increased exploitation rates in the Ocmulgee and Satilla River populations resulted in dramatic declines in overall biomass, especially at lower MLLs (254 and 356 mm, respectively). Therefore, in systems where introduced flathead catfish represent an important recreational fishery but have dramatically reduced the abundance of native fishes through predation, minimal protection is recommended. We contend that rapid growth of introduced flathead catfish has major implications for their management and the conservation of native fishes.
Elevated liver and skin tumor prevalence has been reported in brown bullhead Ameiurus nebulosus from the tidal Anacostia River, Washington, D.C. Movement data are needed to effectively use tumor prevalence as an indicator of habitat quality. We used ultrasonic telemetry to verify the residency of 40 adult brown bullheads (250–310 mm total length) in the Anacostia River during summer 2000, spring 2001, and fall–winter 2001–2002. During summer (10 fish tagged), fish remained within 500 m of their capture–release location, and their mean 95% minimum area polygon (MAP) and linear home ranges were 4.5 ha and 0.50 km. During spring (12 fish tagged), most fish traveled upstream of the capture–release location as water temperatures increased; they were approximately 1 km upriver by the end of the season. Mean 95% MAP and linear home ranges in spring were 19.7 ha and 2.1 km. During fall–winter (18 fish tagged), fish released in the river remained within 4.2 km upstream and 3.1 km downstream of their capture– release location, and their mean 95% MAP and linear home ranges were 15.9 ha and 2.1 km. In comparison, the 95% MAP and linear home ranges of fish released in Lake Kingman (a tidal freshwater impoundment of the Anacostia) were 5.8 ha and 0.58 km. No fish were located outside of the Anacostia River. We conclude that adult brown bullheads were resident in the system throughout the year.
We developed and validated methods for estimating the daily age of age-0 channel catfish Ictalurus punctatus. Two clutches of channel catfish eggs were hatched in the laboratory; subsequently, one was stocked in a 186-m 2 earthen nursery pond and the other in a 757-L outdoor circular tank. Before stocking, subsamples of fish were collected at swim-up and 3 d after swim-up to evaluate early ring formation. Fish were sampled from the pond and tank on eight occasions ranging from 30 to 119 d posthatch. Distinct differences in early ring formation were found between yolk sac and free-swimming larval stages. Mean ring count and known age were closely related for tank-and pond-raised fish, indicating that daily ring deposition occurred in the otoliths of age-0 channel catfish up to 119 d posthatch. The accuracy of daily age estimation was similar between tank and pond samples, and daily ring counts were considerably accurate up to 60 d posthatch. Pond-raised fish were more difficult to age than tank-raised fish, which we attributed to ring compression resulting from slower growth among pond-raised fish after 30 d. The total length of tank-and pond-raised fish was positively related to otolith size; however, the slopes of the relationships between fish length and otolith radius were different between treatments. Therefore, we could not confirm that the relationship between fish length and otolith size was directly proportional for age-0 channel catfish. We encourage researchers to use this aging technique to determine how abiotic and biotic factors influence early life history characteristics and ultimately the population dynamics of catfishes (Ictaluridae).
We validated techniques for estimating the daily age of young‐of‐the‐year Alligator Gar, Atractosteus spatula. Alligator Gar eggs were hatched and larvae were grown in aquaria and then transferred to an outdoor artificial stream. Fish were sampled from 21 d to 118 d posthatch. Sagittal otoliths were extracted from each fish, and each otolith was embedded in a clear epoxy resin. Otoliths were sectioned along a transverse plane, sanded with 600‐grit sandpaper to reveal daily rings, and then polished with 1500‐grit sandpaper. We estimated the daily age of each otolith three times, making each estimate in random order without reference to known ages. The mean of the three counts for each otolith was considered the final age estimate. Daily age estimates of 50 Alligator Gar (21–118 d old, 43–458 mm total length) were closely related to known fish ages, validating daily ring deposition. Absolute error in age estimates increased after 62 d posthatch; 68% of the estimated ages were within ±3 d of the known age through 62 d, whereas only 26% of the estimated ages were within ±3 d of the known age from 76 to 118 d posthatch. However, mean estimates for each cohort were within 5 d of known age through 104 d posthatch. Daily increments near the core were difficult to identify, but later increments were more discernable and deposited in a regular pattern. A significant relationship was also identified between fish total length and otolith radius (P < 0.01), indicating that estimates of growth histories should be reliable. We encourage researchers to utilize our aging technique to estimate hatch dates, the timing and frequency of hatching, and early growth rates of Alligator Gar in wild populations. This early life history information will be valuable in enhancing management and conservation of this species. Received March 21, 2014; accepted July 16, 2014
Our objective was to compare the ability of brown bullheads Ameiurus nebulosus to tolerate the implantation of ultrasonic transmitters with different coatings. A total of 14 brown bullheads were surgically implanted with ultrasonic transmitters; 7 transmitters were coated with paraffin wax and 7 with Scotchcast, an inert epoxy resin. Six brown bullheads were held as controls with no surgical procedures. Fish were held for 75 d in a flow‐through, gravity‐filtered series of tanks and monitored for transmitter expulsion, growth (i.e., percent relative weight change), condition (i.e., relative weight), and mortality. All fish with paraffin‐coated implants retained their transmitters for the duration of the experiment, whereas two fish with Scotchcast implants expelled their transmitters within 50 d. All fish in the experiment survived, and the implanted fish exhibited growth and condition similar to those of the controls. On the basis of these results, we conclude that brown bullheads tolerate implantation of paraffin‐coated transmitters and this attachment method may be used for brown bullheads in telemetric field studies.
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