Britt W. Bumguardner

Toxicity of Oxytetracycline and Calcein to Juvenile Striped Bass

Abstract Acute toxicities of oxytetracycline hydrochloride (OTC) and calcein to juvenile striped bass Morone saxatilis (48 ± 5 mm total length) were determined by immersion. Fish were held in test solutions for 6 h, then placed in clean water and observed for 96 h post-exposure. Both OTC and calcein bind to calcium and fluoresce under ultraviolet light, which makes them useful for marking bony structures of fish. Information on toxicity of these chemicals to juvenile striped bass will help establish maximum concentrations that can be used to mark hatchery fish stocked for population enhancement or establishment. The no-observed-effect concentration (NOEL), 96-h LC 10, and LC50 (concentrations lethal to 10 and 50% of test fish) values for the 6-h chemical exposure were 447, 322, and 597 mg/L for OTC and 125, 160, and 240 mg/L for calcein.

Genetic Identification of Hatchery-Released Red Drum in Texas Bays and Estuaries

Abstract The stock enhancement program for red drum Sciaenops ocellatus in Texas annually releases from 25 to 30 million fingerlings into Texas bays and estuaries and represents one of the largest such programs for marine fishes worldwide. We used 16 nuclear-encoded microsatellites and a 370-base-pair fragment of the mitochondrial DNA (mtDNA) D-loop to assign red drum sampled from two bays along the Texas coast to either hatchery or wild origin. A total of 30 hatchery-released fish were identified among 321 red drum belonging to three year-classes sampled from Galveston Bay, while a total of 11 hatchery-released fish were identified among 970 red drum belonging to four year-classes sampled from Aransas Bay. Allelic richness (microsatellites) was significantly lower among hatchery-released fish than among hatchery broodfish and wild fish. Similarly, the expected number of mtDNA haplotypes in hatchery-released fish (based on simulation analysis) was significantly lower than that expected in a random sample ...

Marking Subadult Red Drums with Oxytetracycline

Abstract Otoliths, scales, and spines of two recaptured subadult red drums Sciaenops ocellatus (514 and 537 mm total length) were examined for induced fluorescence 10 months after injection with oxytetracycline–HCl at about 50 mg/kg body weight. Both fish exhibited fluorescence in sagitta, lapillus, and asteriscus otoliths, scales, and dorsal and anal spines. Sagittae from both fish had formed an annulus between release and recapture.

Use of Scale Circuli Pattern Analysis to Differentiate between Hatchery and Wild Red Drum

Abstract In 1983, the Texas Parks and Wildlife Department initiated a stock enhancement program that released up to 20 million red drum Sciaenops ocellatus annually. To evaluate the contribution of hatchery production to the fishery, scale pattern analysis was used to differentiate between hatchery-reared and wild fish. Scale patterns from 30–150-d-old hatchery-reared red drum fingerlings (13–35 mm total length, TL) from two hatcheries and wild red drum juveniles (<121 mm TL) were analyzed to establish a linear discriminant function. Accurate identification of 30-d-old hatchery-reared red drum ranged from 61–64%, but decreased to 35% for 60–150-d-old fish; classification rates for wild fish ranged from 63% to 70%. Correct classification of 30-d-old hatchery fish was significantly better than chance, but correct classification of wild fish was only significantly better than chance at one hatchery. Linear discriminant functions were used to evaluate variation between spring and fall hatchery-reared red drum...

Analyses of six years of spotted seatrout (Cynoscion nebulosus) pond culture trials

Abstract Spotted seatrout (Cynoscion nebulosus) pond culture trials (52) were conducted on the central Texas coast from 1983 through 1988. All ponds were stocked with 2-day-old larvae at 45 000 to 2 075 000/ha, 9 to 28 days after initial filling and fertilization. Zooplankton, dissolved oxygen concentration, salinity, and temperature were routinely sampled throughout the culture period. Ponds were harvested 20 to 30 days after stocking. Stepwise multiple regression analyses were used to examine the effect of 38 independent variables associated with stocking density, the length of the culture period, fertilization, water quality, and zooplankton densities on percent harvest, number of fish harvested/ha, and kg of fish harvested/ha day−1 of culture. Mean temperature, mean polychaete larvae densities for the culture period, and minimum dissolved oxygen concentration observed explained 69% of the variance in percent harvest. Mean temperature, stocking density, and mean polychaete larvae densities in the second, third, and fourth week after stocking explained 79% of the variance associated with number of fish harvested/ha. Variation observed in kg of fish harvested/ha day−1 of culture was best explained (R2 = 0.76) by mean temperature, stocking density, and mean polychaete larvae densities in the first and fourth week after stocking. Polychaete larvae density, especially during the latter stages of culture, was statistically the most important factor associated with production of spotted seatrout from larvae to ≈ 30 mm TL fingerlings.

The Critical Thermal Maximum of Juvenile Red Drum Reared for Out-of-Season Stocking in Texas

Abstract Hatchery-propagated red drum Sciaenops ocellatus are released by the Texas Parks and Wildlife Department (TPWD) during the spring, summer, and fall to supplement natural stocks. Reported success of red drum stocked out of season in summer has been low or nonexistent; several potential causes, including mortality due to high temperatures, have been suggested. The present study was devised to determine the critical thermal maximum (CTM) of pond-raised juvenile red drum that had previously been exposed to diurnal temperatures of the summer season. Laboratory studies designed to mimic the rate of temperature increase (0.25°C per hour) typical of TPWD rearing ponds were used to examine rates of mortality in juvenile red drum that were collected from three separate ponds exposed to the ambient fluctuating temperatures of the summer season. The CTM (temperature that was lethal to 50% of the test fish [LT50]) was significantly lower (P < 0.0001) for two of the fish trials (LT50 = 37.1°C and 37.0°C) than ...

Effect of salinity on the upper lethal temperature tolerance of early-juvenile red drum

Previous work investigating the temperature tolerance of juvenile red drum ranging 18-50mm TL found evidence for positive size dependence (smaller fish less tolerant to higher temperatures) suggesting smaller size classes (<18mm TL) potentially may succumb to extreme summer water temperatures. Here, we explored the upper lethal temperature tolerance (ULT) in smaller-sized red drum which ranged from 10 to 20mm TL across multiple salinities to further understand the thermal limitations of this propagated game fish. In order to investigate the combined effect of temperature and salinity on ULT, temperature trials were conducted under three levels of salinity which commonly occur along the coast of Texas (25, 35, and 45ppt). The rate of temperature increase (+0.25°C/h) was designed to mimic a natural temperature increase of a summer day in Texas. We determined that the lethal temperature at 50% (LT50) did not differ between the three salinities examined statistically; median lethal temperature for individuals exposed to 25ppt ranged from 36.4 to 37.7°C, 35ppt ranged from 36.4 to 37.7°C, and 45ppt ranged from 36.1 to 37.4°C. Further, LT50 data obtained here for early-juvenile red drum did not differ from data of a similar experiment examining 25mm TL sized fish.

Lower Lethal Temperature for Juvenile Cobia Rachycentron Canadum

Cobia are a migratory marine species that have recently gained popularity as foodfish in the aquaculture market and for stocking. Unfortunately, when culturing these species, aquaculturalists may unknowingly expose these fish to temperature extremes not normally experienced in situ. We set out to test for the critical thermal minimum temperatures of juvenile cobia by exposing them to a simulated freeze, at a drop rate of 0.33°C per hour. We observed and documented behavioral effects due to low temperature exposure using criteria for loss of equilibrium and death. We determined that the median temperature for loss of equilibrium was 12.1 ± 0.40°C and the median lethal temperature was 9.7 ± 0.28°C for low temperature tolerance. We recommend that precautions be taken well before water temperatures reach 13°C in a freeze scenario.

Effects of three cold weather event simulations on early life stages of Southern Flounder (Paralichthys lethostigma)

ABSTRACT To determine the minimum age/size at which Southern Flounder, Paralichthys lethostigma, can safely be moved to outdoor rearing facilities in Texas, we examined survival of simulated temperature drops in two distinct life stages: premetamorphic larvae and two size classes of postmetamorphic juveniles (small = 9.8 ± 0.3 mm in TL; large = 19.7 ± 0.6 mm). Temperature was lowered by −0.33°C/h to 4°C, 7°C, or 10°C, held for 48 h and then raised at +0.33°C/h back to normal rearing temperature. Fish were monitored daily for survival. Larger postmetamorphic flounder had high survival for all temperature treatments (89%–100% survival), whereas both premetamorphic larvae and smaller postmetamorphic juveniles had low survival (<30%) for all temperature treatments.

Critical Thermal Maximum of Juvenile Spotted Seatrout (Cynoscion nebulosus) Reared for Summer Stocking in Texas

The critical thermal maximum of juvenile spotted seatrout (SL range 18–33 mm) was determined using a temperature increase of +0.26°C per hour. The critical thermal maximum (water temperature that was lethal to 50% of the test fish [LT50]) for trial 1 was LT50 = 38.8°C, LT50 = 39.4°C for trial 2, and LT50 = 38.9°C for trial 3. Critical thermal maximums differed significantly (P < 0.05) between trials 2 and 3, whereas trial 1 did not differ among trials. This difference correlated with body size, where fish in trial 2 were significantly larger (P < 0.05) (mean = 27.6 ± 2.0 mm in SL) (mean ± SE) than the fish of trials 1 (mean = 23.1 ± 0.5 mm in SL) and 3 (mean = 21.5 ± 0.7 mm in SL), suggesting positive size dependence in the critical thermal maximum.