Robert R. Vega

Ecophys.Fish: A Simulation Model of Fish Growth in Time-Varying Environmental Regimes

Ecophys.Fish is a deterministic STELLA® model for simulating rates of fish growth in environmental regimes that have simultaneous temporal variation in food, oxygen, temperature, pH, and salinity. The purpose of this article is to introduce Ecophys.Fish to those who might want to use it as a framework or starting point for applications of their own. We believe our model, although focused in autecology, will prove useful at organizational levels both below and above the individual fish. Ecophys.Fish is a quantitatively explicit interpretation of concepts originally formalized by F.E.J. Fry, almost 60 years ago. Frys “physiological classification of environment” and his concept of “metabolic scope for activity” were coupled with conventional bioenergetics to provide the models theoretical basis. The models inputs are initial size of fish, and time series of temperature, pH, dissolved-oxygen concentration (DO), salinity, and food availability and its energy content. Outputs are food consumption, oxygen consumption, waste production, energy content of fish biomass, and growth. Indirectly, the output is a measure of relative fitness of the fish-environment system to support fish growth. Two variants of the model represent the euryhaline red drum (Sciaenops ocellatus) and the freshwater bluegill (Lepomis macrochirus). Ecophys.Fish had its beginnings in laboratory experiments with juvenile red drum. These experiments enabled definition of functions and their parameterization, leading to a working model that effectively simulated growth of red drum in various pond and estuary trials with caged fish. Subsequently, Ecophys.Fish was converted to simulate growth rates of caged bluegill involved in stream ecoassays. The latter work confirmed the models generality and the utility of automated routine respirometry for empirically estimating a key model parameter. Ecophys.Fish comprises an effective tool for resolving sources of variation in fish growth, even in natural systems with high levels of environmental variability. Moreover, the model has utility for probing biological and ecological mechanisms underlying fish growth and production. Finally, Ecophys.Fish is capable of producing rich hypotheses, e.g., 1) the optimum temperature for growth decreases whenever DO, food availability, or energy density of available food is limiting; 2) with unlimited DO and food availability, the optimum temperature for growth increases with increasing fish size but only when energy density of food is limiting; and, 3) when neither availability nor energy density of food is limiting, growth can be much faster under diel-cycling regimes of temperature and DO than under the optimum constant temperature/DO regime. Under Ecophys.Fish, environmental regimes that are best for survival are not necessarily those that are best for growth.

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 ...

Genetic Effective Size in Populations of Hatchery-Raised Red Drum Released for Stock Enhancement

Abstract Genetic analysis of progeny from 13 spawning events occurring over a 2-week period in a Texas Parks and Wildlife Department (TPWD) hatchery for red drum Sciaenops ocellatus during the spring of 2002 and hatchery spawning and release records over the 2003 spawning season were used to estimate the average genetic effective size of an average spawn and an average hatchery-released population. The purpose of this study was to assess the potential for a Ryman-Laikre effect in the TPWD red drum stock enhancement program. Genetic analysis revealed that 16 of 27 dams (59.2%) and 16 of 18 sires (88.9%) spawned at least once. The average effective size (Ne ) for a single spawn was 2.59, approximately 43% less than the maximum Ne (4.55) predicted if all possible mating (dam × sire) combinations had occurred and family size per mating combination had been equivalent. The reduction in Ne stemming from the actual number of mating combinations was approximately 34% and appeared to be due primarily to nonspawnin...

Spawning frequency of brood dams and sires in a marine fish stock-enhancement hatchery

Parentage analysis, employing five hypervariable microsatellite markers, was used to follow spawning patterns of red drum Sciaenops ocellatus broodfish in two spawning tanks through most of a calendar year in a marine fish hatchery dedicated to stock enhancement. Five of six dams and all four sires spawned at least once during the year. Variation in dam and sire spawning incidence and in number of progeny produced per dam and per sire translated into reduced genetic effective size (N e) per spawn by 40·6% in one tank and 50·8% in the other.

Effects of Temperature and Feed Energy on the Performance of Juvenile Red Drum

Abstract We tested the hypothesis that the growth of fish exposed to high temperatures can be limited by available food energy whereas that of fish exposed to low temperatures can be limited by their metabolic capacity to exploit the available food energy. Under laboratory conditions we evaluated growth (%/d) and marginal metabolic scope (MMS; L·g−1·h−1) of juvenile red drum Sciaenops ocellatus exposed to two levels of dietary energy, low (LE; ∼4.1 kJ/g) and high (HE; ∼15.9 kJ/g), and to three temperatures, approximately 19, 25, and 29°C, for a period of 6 weeks. Growth rate and MMS increased with temperature, but only growth rate increased with dietary energy and then only at the higher two temperatures. The simulation model Ecophys. Fish was employed to elucidate experimental results potentially confounded by interactions between fish weight and the controlling effects of temperature on metabolism. The simulated and observed results both showed that performance is enhanced at higher temperatures, especi...

Catch-and-Release Mortality of Spotted Seatrout in Texas: Effects of Tournaments, Seasonality, and Anatomical Hooking Location

Abstract The purpose of this study was to assess initial and delayed mortality of spotted seatrout Cynoscion nebulosus captured during live-release tournaments. Additionally, we examined spotted seatrout mortality as a function of season and anatomical hooking location. We assessed tournament-related mortality at 10 live-release fishing tournaments held in four Texas bays—Galveston, Matagorda, Aransas, and Upper Laguna Madre—from February 2004 to April 2006. Combined overall mean mortality was 22.9%, mean initial mortality (percent of dead fish brought to weigh-in) was 10.4%, mean delayed mortality (percent of fish that died in tournament holding tanks) was 14.1%, and delayed short-term mortality (percent of fish that died during a 14-d observation period in laboratory tanks) was 1.9%. To assess seasonal mortality, we examined a total of 364 spotted seatrout captured by hook and line from July 2004 to June 2005 using replicated 3.5-m3 field enclosures for 72 h. Overall mortality for the seasonal study was...

Heritability of Cold Tolerance in Red Drum

Abstract Heritability (h 2) of cold tolerance was estimated for red drum Sciaenops ocellatus, an economically important sciaenid fish in the southern USA. Nineteen families were generated via environmentally induced spawning of multiple sets of five broodfish (three dams × two sires) and were mixed in three common-garden replicate tanks for cold tolerance challenge. All offspring were assigned postmortem to parents based on genotypes at nuclear-encoded microsatellites. The cold tolerance trial was initiated when offspring were 230–251 d old (total length mean ± SD = 182 ± 26 mm). Temperature was decreased progressively from 25°C to 3°C over a 30-d period and was maintained at an average of 3.1°C until all fish expired. Mortality began when temperature reached 5°C. Cold tolerance of individual fish was quantified based on survival time and a cooling-degree-hours (CDH) index. The h 2of cold tolerance was estimated using an animal mixed model and a restricted maximum likelihood algorithm. The h 2 (mean ± SE)...

Development of primers for 29 microsatellite loci in spotted seatrout (Cynoscion nebulosus)

Twenty-nine microsatellites were isolated from genomic DNA of spotted seatrout (Cynoscion nebulosus). The microsatellites were screened across 10–25 individuals from a single population sampled in the Lower Laguna Madre, Texas. All microsatellites were polymorphic with the number of alleles per locus ranging from 3 to 25. Expected heterozygosity ranged from 0.34 to 0.96. No deviations from Hardy–Weinberg equilibrium or linkage disequilibrium were observed following correction for multiple simultaneous tests.

Reproductive Variance of Brood Dams and Sires used in Restoration Enhancement of Spotted Seatrout in Texas Bays and Estuaries

AbstractSpawning patterns and reproductive variance of Spotted Seatrout Cynoscion nebulosus dams and sires at two restoration enhancement facilities in Texas were assessed across a spawning year by using parentage analysis based on 12 variable microsatellite loci. In total, 72.6% of all dams and sires contributed to at least one spawning event, although in contrasting patterns. Across all spawning events assayed, more sires contributed to each spawn, on average, than did dams; dams had considerably higher variance in reproductive success than sires. Dams alternatively had a higher average contribution to the number of progeny from a single spawn but also a much higher variance in the number of progeny produced per spawn. The variation in the number of progeny produced per dam and per sire and the number of actual mating combinations led to an average reduction of 64.3% in the genetic effective population size (Ne) per spawn relative to the maximum Ne that would be expected if (1) all possible dam × sire m...