Michael R. Denson

Broodstock management and spawning of southern flounder, Paralichthys lethostigma

Collaborative studies are underway in South Carolina (SC) and North Carolina (NC) to control reproduction of southern flounder, Paralichthys lethostigma. Although cultured broodstock are being developed, work to date has been with wild caught adults held in captivity for at least 1 year. Shortly after capture, wild adults should be treated to control diseases and parasites, especially Amyloodinium sp. and fish lice, Argulus sp. Induced spawning using only photothermal control has not occurred, but GnRHa implants have been successfully used to induce ovulation and allow strip-spawning. In addition, during 1997, photothermal conditioning coupled with 100 μg GnRHa implants resulted in successful tank-spawning. During a 99-day period, eggs were collected on 64 days and lowering temperature was shown to inhibit spawning. On days that spawning occurred, mean number of eggs collected was 277,844 (±177,714) and mean fertility was 32.8% (±25.2%). Total number of eggs collected was 17,782,000. Females used in the study were ≥5 years old while the males were ≥3 years old. Fish had been in captivity for ≥1.5 years. The spawning success achieved using the combination of photothermal conditioning and GnRHa implants resulted in less stress to the fish, higher egg production and an extended spawning period. Use of photothermal conditioning coupled with tank-spawning techniques should allow year-round spawning of southern flounder. This should facilitate more rapid development of a culture technology for this species.

Retention of Oxytetracycline-Induced Marks on Sagittae of Red Drum

Abstract In a pilot-scale stocking program, juvenile red drum Sciaenops ocellatus were immersed for 4 h in a 500-mg/L active solution of oxytetracycline hydrochloride (OTC) and 15-g/L salinity water at a temperature of 26.2°C to mark the otoliths before release. A portion of the treated fish was retained to determine marking success and mark retention. Retained fish were held in outdoor tanks supplied with flow-through estuarine water from Charleston Harbor, South Carolina, and fed commercial trout diets daily. During a 4.4-year period, subsamples of treated fish were regularly sacrificed, and their sagittae were removed, sectioned, and examined under an epifluorescent microscope to validate presence of a mark. Because of interference from autofluorescence, OTC marks were not detectable on sagittae from fish sampled 56 d after immersion (N = 4). However, a mark was visible on 100% of sagittae examined from treated fish sampled on nine occasions from 73 to 1,618 d after immersion (N = 46). In a blind test,...

Communications: Tank Culture of Larval Sunshine Bass

Abstract In 1995, two studies were conducted at the Marine Resources Research Institute, Charleston, South Carolina, that focused on development of techniques to intensively rear larval sunshine bass, the hybrid of female white bass Morone chrysops and male striped bass M. saxatilis. During the first study, the rotifer Brachionus plicatilis was shown to be an acceptable first-food when fed at 10 organisms/mL in static black tanks receiving high surface illumination (mean, 600 lx). It was further demonstrated that larvae could be switched to a diet of just nauplii of Artemia sp. by at least day 8 post-hatch. At the conclusion of the 8-d study, larvae fed Artemia nauplii earlier were significantly larger (9.12 mm total length, TL) than larvae fed rotifers through day 7 posthatch (6.71 mm TL). However, there were no survival differences (mean, 67.2%). During the second study, supplementation of the Artemia nauplii diet with a commercial larval feed offered no advantage to 12-d-old larvae, which had similar s...

Pond Culture of Larval and Juvenile Cobia, Rachycentron canadum, in the Southeastern United States

Abstract The potential of growing larval and juvenile cobia, Rach-ycentron canadum, in ponds was investigated. Larval cobia, obtained from tank spawning of wild-caught adults, were stocked 48-72-h post-hatch at a rate of 700,000/ha into three fertilized 0.25-ha ponds. At one week post-stocking (WPS), fish were observed consuming formulated feed. Growth was rapid, with specific growth rates (SGR) ranging from 12.5-19.2% body weight/day. At harvest (5 WPS) fish reared in two ponds weighed 7.9 and 9.3 g and total length (TL) was 118.9 and 129.3 mm, respectively (all fish reared in remaining pond died the night prior to harvest due to aerator failure). Feed conversion ratio (FCR) was 3.8 for both ponds and survival was 5.3 and 8.5%. Low survival rates were thought to be due primarily to cannibalism. Immediately after harvest, fish were restocked into two 0.25-ha ponds at a stocking rate of 14,400/ ha. Fish were fed formulated, pelleted feeds. Growth was rapid up to ∼9 WPS, after which pond water temperatures declined. Ponds were harvested at 13 and 15 WPS, respectively. Final weight of fish was 309.9 and 362.5 g. Final TL was 343.1 and 355.7 mm. FCR was 3.8 and 4.5 and survival was 27.5 and 30.5%. Major losses of fish were associated with avian predators and possibly a toxic algal bloom. Results of trials indicate that cobia larvae and juveniles can be reared in pond-based culture systems, however additional research is needed to refine this approach.

Year-Class Component, Growth, and Movement of Juvenile Red Drum Stocked Seasonally in a South Carolina Estuary

Abstract Red drum Sciaenops ocellatus have been classified by the Atlantic States Marine Fisheries Commission as overfished in the Atlantic off the southeastern USA. A study was conducted to evaluate stocking hatchery-reared fish as a management tool to increase abundance of red drum in South Carolina estuaries. Multiple groups of juveniles, at mean sizes of 22–56 mm total length, were released after being marked by immersion in 15 g/L salinity brackish water containing oxytetracycline HCl (500 mg/L active). Fish were released into a small (535-ha) part of the available nursery habitat (total = 25,000 ha) in the Port Royal Sound estuary each fall and spring from fall 1995 through spring 1997. During fall 1995 and spring 1996, 347,000 fish were stocked; during fall 1996 and spring 1997, the number was 1,228,000. Movement of hatchery fish from the release site was monitored for at least 2 years after release. Overall, hatchery fish accounted for 19.0% of the 627 fish (age 0 to age 2) captured from the 1995 ...

Assessing Red Drum Juvenile Stocking in a South Carolina Estuary Using Genetic Identification

Abstract The South Carolina Department of Natural Resources has been stocking red drum Sciaenops ocellatus since 1988 to evaluate parameters critical to their successful survival and recruitment in South Carolina estuaries. From 1999 to 2002, between 600,000 and 1,000,000 juvenile red drum were stocked each year in two tributaries of Charleston Harbor. The harbor and each tributary were partitioned into three independent strata and randomly sampled monthly for two decades, allowing population trends before, during, and after stocking to be evaluated. Using microsatellite-based parentage analysis, we examined the contribution of stocked age-0 juvenile red drum (15–60 mm total length) to the local population 1 year after release by using fishery-independent sampling. Analysis of these data showed that the highest contributions (88.9%) were close to the stocking site in years with low natural recruitment, whereas in years with high natural recruitment, contributions were lower and stocking was less effective...

Small Marine Reserves May Increase Escapement of Red Drum

Abstract An experimental stock enhancement program was conducted in Port Royal Sound estuary, South Carolina, in which cultured juvenile red drum (Sciaenops ocellatus, 2–3 cm TL, ∼40 days old) were released into a system of shallow tidal creeks that flow into the Colleton River. All fish were immersed in oxytetracycline (OTC) prior to release to produce an identifiable, chemical mark on the otoliths. The release area was typical of primary nursery habitat in this region. For four years post-stocking, fish were collected throughout the sound using hook and line, spear, and trammel net. Otoliths were examined for OTC marks to determine which fish were of hatchery origin. It was found that while dispersal was substantial, many stocked fish stayed in the general area of release (1.8 × 3.2 km) until reaching the age of maturity (∼age 3) when they left the estuary, and at all ages they were mixed with wild fish. This suggests that relatively small areas containing the appropriate suite of habitat types could be...

Low-Temperature Tolerance of Juvenile Spotted Seatrout in South Carolina

AbstractSpotted Seatrout Cynoscion nebulosus are vulnerable to mortality in winter when water temperature decreases rapidly. Temporary fishery closures in response to population declines should be based on a thorough understanding of the magnitude of winter mortality. We used three methods to estimate the low-temperature tolerance of Spotted Seatrout: the chronic lethal method (CLM) and the acclimated chronic exposure (ACE) method using both static and fluctuating temperatures. All three methods use an environmentally realistic temperature change of 1°C/d. Fish acclimated to 14°C (n = 24) for 10 d and subsequently exposed to constantly declining temperatures using the CLM experienced loss of equilibrium at a temperature of 3.57 ± 0.24°C (mean ± SD) and mortality at a temperature of 3.08 ± 0.31°C. The ACE method, which uses changing temperatures until a base temperature is reached, was used to evaluate how Spotted Seatrout are affected by prolonged, sublethal temperatures. The ACE method was performed with...

Genetic Population Structure of US Atlantic Coastal Striped Bass (Morone saxatilis)

Genetic population structure of anadromous striped bass along the US Atlantic coast was analyzed using 14 neutral nuclear DNA microsatellites. Young-of-the-year and adult striped bass (n = 1114) were sampled from Hudson River, Delaware River, Chesapeake Bay, North Carolina, and South Carolina. Analyses indicated clear population structure with significant genetic differentiation between all regions. Global multilocus F ST was estimated at 0.028 (P < 0.001). Population structure followed an isolation-by-distance model and temporal sampling indicated a stable population structure more than 2 years at all locations. Significant structure was absent within Hudson River, whereas weak but significant genetic differences were observed between northern and southern samples in Chesapeake Bay. The largest and smallest effective striped bass population sizes were found in Chesapeake Bay and South Carolina, respectively. Coalescence analysis indicated that the highest historical gene flow has been between Chesapeake Bay and Hudson River populations, and that exchange has not been unidirectional. Bayesian analysis of contemporary migration indicated that Chesapeake Bay serves as a major source of migrants for Atlantic coastal regions from Albemarle Sound northward. In addition to examining population genetic structure, the data acquired during this project were capable of serving as a baseline for assigning fish with unknown origin to source region.

Differentiating between Hatchery and Wild Red Drum by the Position of First Annulus on Sagitta

Abstract An otolith-based method that permits rapid and accurate differentiation between hatchery-produced and wild red drum Sciaenops ocellatus was identified. Sagittae from several year-classes of hatchery-produced (both stocked and captive) and wild red drum more than 18 months old were examined. Hatchery fish were spawned in spring, about 6 months before the natural spawning season. On sagittae, the distance from the core to the first annulus (mean = 1,247 μm) for three year-classes of wild fish collected before hatchery releases was significantly larger (P < 0.001) than that for three year-classes of hatchery fish (mean = 690 μm). Although there were differences in core–annulus distance among year-classes of hatchery fish, neither the 99% confidence intervals nor the core–annulus distance ranges overlapped for hatchery and wild fish. Springs-pawned red drum deposited an annulus during the first winter, whereas wild fish deposited an annulus during the second winter, at an age of approximately 18 mont...