J. Holt Williamson

Cryopreservation of Sperm of the Endangered Razorback Sucker

Abstract The endangered razorback sucker Xyrauchen texanus is endemic to the Colorado River system in western North America and is threatened with extinction because of limited recruitment. To assist in management and recovery efforts, we developed methods for the cryopreservation of sperm, evaluated the influence of various factors on motility of thawed sperm, and examined the effect on fertilization of cooling rate and the addition of caffeine. Sperm samples cryopreserved with 10% methanol (MeOH) had significantly higher postthaw motility than did samples preserved with 5% or 20% MeOH or with 5% or 10% dimethyl sulfoxide, N, N-dimethylacetamide, glycerol, propylene glycol, or ethylene glycol. Sperm samples cryopreserved in 0.5-mL and 2.5-mL straws had significantly higher postthaw motility than did samples cryopreserved in 0.25-mL straws. Exposure to 10% MeOH for up to 30 min did not significantly influence sperm motility before freezing or after thawing. Cooling rate (−21°C/min or −91°C/min) did not si...

Multispecies hybridization among native and introduced centrarchid basses in central Texas.

Abstract Allele-frequency differences at 11 polymorphic protein loci provided discrete genetic markers with which to estimate the extent of hybridization among native and introduced centrarchid basses in central Texas streams. Native Guadalupe bass Micropterus treculi and northern largemouth bass M. salmoides salmoides now coexist with introduced Florida largemouth bass M. s. floridanus and smallmouth bass M. dolomieui in these streams. Interspecific hybridization was detected in three of four populations from the Blanco and San Marcos rivers, hybrids making up at least 31.8% of the individuals sampled. Complex hybridization patterns were evident, because F1, F2, and backcross hybrids were detected. At least one individual exhibited genetic markers of largemouth, smallmouth, and Guadalupe bass. Extensive multispecies hybridization threatens the survival of the endemic Guadalupe bass.

An aquacultural evaluation of Florida, northern, and hybrid largemouth bass, Micropterus salmoides

Abstract Largemouth bass (Centrarchidae) strain evaluation experiments conducted to determine suitability of this species for aquaculture are summarized. Strain comparisons of two subspecies, Micropterus salmoides salmoides (northern) and M. s. floridanus (Florida), and the two F t hybrids were characterized under an intensive culture regime. Food trainability, growth, survival, feed conversion, stress response, response to low temperature, and responses to low dissolved oxygen coupled with water quality perturbations were characterized. All strains were reared communally and separately and tested for the various performance characters after electrophoretic identification. Northern largemouth bass grew faster, resisted net-stress better, tolerated ammonia in the water better, trained to eat pelleted food more readily, tolerated low temperatures and low oxygen better, and converted food to biomass more efficiently than the other three strains of largemouth bass tested.

Growth and Catchability of Northern, Florida, and F, Hybrid Largemouth Bass in Texas Ponds

Abstract Fish from two genetically identified populations of largemouth bass Micropterus salmoides, representing the northern subspecies M. s. salmoides (N × N) and the Florida subspecies M. s. floridanus (F × F), and their reciprocal F1 hybrids (F × N and N × F; female represented first) were stocked in 0.04–0.48-hectare ponds and evaluated for growth, condition, and percent survival during the second year of life. Angling and seine-capture vulnerability were also examined. The F × N cross was significantly heavier and had a significantly higher relative weight (100 [individual weight/standard weight at length]) than the other crosses at the end of the study. The F × F cross was significantly shorter, weighed less, and was in poorer condition than all other crosses. The N × N cross was generally more susceptible to angling than the F × F cross. The F × F cross was significantly less vulnerable to seine capture than the other three crosses.

Genetic Marker Identification in Largemouth Bass with Electrophoresis of Low-Risk Tissues

Abstract Electrophoretic genotyping is a contemporary technique that enables aquaculturists and fishery managers to distinguish between domestic and native stocks of largemouth bass Micropterus salmoides and to monitor gene flow between them. Analysis of low-risk tissue samples (erythrocytes, blood plasma, caudal and pelvic fin, and scale-epithelial tissue) allows investigators to obtain considerable genetic information with minimal loss of performance by individual fish. We have identified at least 64 enzyme locus products in Florida, northern, and intergrade strains of largemouth bass by using invasive biopsy or necropsy. Polymorphic loci account for approximately one-third of the loci examined. Low-risk tissue samples allowed adequate electrophoretic resolution of 44 (69%) of the 64 gene products examined. Of the 23 polymorphic loci thus far identified in largemouth bass, at least 16 can be resolved from blood or fin tissues or both. Thus, using only tissue samples that do not significantly debilitate ...

Comparing Training Success of Two Strains of Largemouth Bass

Abstract A study was conducted to determine if fingerlings of two strains of largemouth bass, Micropterus salmoides, differed significantly in acceptance of formulated feed. The San Marcos (Marion) and Inks Dam (northern) strains of largemouth bass were trained at the San Marcos National Fish Hatchery and Development Center to accept formulated feed, Biodiet, under similar conditions in a simulated production environment. Fingerlings (average total length, 30 mm) that had been reared under similar conditions were stocked at equal densities, in triplicate, in indoor rectangular tanks. They received semimoist pellets, 1.6 mm in diameter, at a rate equal to 15% of the stocked biomass per day throughout the training period. Training success was 23% for the Inks Dam and 43% for the San Marcos strain. The San Marcos strain performed 84% better than the Inks Dam strain under similar conditions. These results appear to support the contention that genetic difference explains to a considerable extent the difference...

Intensive Production of Guadalupe Bass

Abstract A study was conducted to determine if the threatened Guadalupe bass (Micropterus treculi) could adapt to fish hatchery production. Five hormone-injected fish (one female and four males) stocked in a 0.04-hectare spawning pond produced about 1,200 harvestable fingerlings. The fish were size-graded into three classes and stocked into indoor rectangular tanks. Fingerlings, 22-45 mm total length and 0.32-1.02 g, were trained to consume formulated feed in a simulated production environment. They received 1.0-1.5-mm-diameter semi-moist pellets at a rate greater than 48% of the stocked biomass per day throughout the 24-d training period. Training success for the three size classes was 96.4, 97.6, and 100.0%. Growth rates during and following training were similar to those of other Micropterus species. These results indicate that the Guadalupe bass will adapt to fish hatchery conditions and can be produced to supplement depleted native populations.

New Biochemical Genetic Markers for Largemouth Bass

Abstract New electrophoretic analyses have provided additional information concerning intraspecific genetic variation among largemouth bass Micropterus salmoides. Genetic differences, previously unknown, were found among four stocks of largemouth bass, two of them domestic and two of which were one generation removed from the wild. The domestic stocks were derived from intergrade populations of northern and Florida subspecies; one nonintergrade stock represented the northern subspecies M. s. salmoides and the other represented the Florida subspecies M. s. floridanus. More than 60 presumptive loci were electrophoretically examined. At least 11 loci were polymorphic. Of the polymorphic loci, two represented previously known fixed subspecific differences and two or perhaps three represented previously known allele frequency differences. Variation among the stocks at the remaining loci was expressed as allele frequency differences. Allelic polymorphisms restricted in our sample to Florida or intergrade popula...

Field Propagation Techniques for the Endangered Razorback Sucker

Abstract We used plastic bags to incubate, transport, and hatch embryos for specific crosses of razorback suckers Xyrauchen texanus during two spawning seasons on the Colorado River (Nevada–Arizona). Fifty to 2,000 razorback sucker eggs were fertilized in plastic food storage bags for 26 matings in 102 trials. Experimental treatments prevented hatching in all bags, but hatching was observed when fresh milt and viable eggs were used (10–99% hatch). Observation of embryo development and treatment effects was facilitated by the transparency and portability of the bags. Water volume and exchange rates were chosen according to estimated metabolic rates, and the addition of oxygen to the bags was evaluated to increase holding times. Plastic bags were inexpensive and useful for gamete storage, controlled propagation, and transport of gametes, embryos, and fry under field conditions. These techniques are suitable for various applications in studies of reproductive biology, and they are especially suited to geneti...

Communications: Responses of Northern, Florida, and Hybrid Largemouth Bass to Low Temperature and Low Dissolved Oxygen

Abstract Two parental subspecies of largemouth bass (Micropterus salmoides), northern (M. s. salmoides) and Florida (M. s. foridanus), and their reciprocal F1 hybrids were examined for their responses to low temperature and low dissolved oxygen concentrations. The four strains (verified electrophoretically) survived a temperature decrease from 21 to 1°C at a rate of about 1°C/d followed by immediate warming. Among fish maintained at low temperature (2.0 ± 0.4°C; mean ± SE) for 5 d, mortalities were 48% for the Florida fish and 4–5% for the Florida (female) hybrid, compared with zero for the northern fish and the northern (female) hybrid. All four groups showed similar trends in feeding behavior during the temperature treatments. At 22°C acclimation, the residual oxygen concentrations (oxygen concentrations at time of death by hypoxia, during sealed-jar-hypoxia bioassays) were lower in tests with the northern and Florida subspecies than in tests with the hybrids, and were lower for northern than for Florid...