Aquaculture-related Stressors in Scaphirhynchus Sturgeon
The effect of environmental and aquaculture-related stressors on physiological indicators of stress (i.e. plasma cortisol, glucose, and lactate dynamics) in Scaphirhynchus sturgeon was investigated as part of an undergraduate student research project. The stressors investigated were those common in aquaculture settings and included low dissolved oxygen, increased fish densities, and high unionized aqueous ammonia concentration. Increased fish densities were found to increase plasma cortisol levels most.
Efficacy of Aqui-S® 20E as a Sedative for Handling and Cortisol Suppression in Pallid Sturgeon
The primary objectives of this study were to identify the target dose of Aqui-S® 20E for sedation to handleable of pallid sturgeon and to determine cortisol response in sturgeon exposed to the identified target dose in relation to the only FDA-approved fish anesthetic, MS-222. Fish sedated with Aqui-S® 20E had lower plasma cortisol levels following sedation, and rapid sedation and recovery times were achieved with an optimal dose. Aqui-S® 20E appears to be a suitable sedative for use in pallid sturgeon.
San Pedro Fish Oplegnathus insignis Stress Physiology Research: Aquaculture in Chile
As part of a collaborative effort with CORDUNAP, this project seeks to use biotechnological tools to develop a successful San Pedro broodstock culture operation, with the final aim of generating high quality eggs and improving survival and growth throughout the larval and juvenile life stages. This past year’s research effort has focused on identifying basal stress levels of hormonal and metabolic indicators for assessing this species’ ability to adapt to captive culture conditions.
Characterizing Ghrelin as a Regulator of Feeding and Carbohydrate Utilization in Channel Catfish
Ghrelin is known to affect appetite and growth in terrestrial vertebrates, and our research suggests it plays a central role in glucose metabolism in catfish. As such, complete tissue distribution, ontogeny, and effects of endocrine and dietary manipulations were examined. We observed meal-related changes in ghrelin expression indicative of ghrelin’s involvement in appetite regulation, and changes in ghrelin expression related to carbohydrate intake. These findings suggest ghrelin is an important regulator of appetite and carbohydrate metabolism in fish.
Catfish Hatchery Management
Hatching rates of individual channel catfish spawns in commercial and research hatcheries are highly variable. To address this problem, several studies were conducted to define normal embryo development, and determine the effects of temperature, calcium, transport, and handling on hatching success. Normal embryo development was documented photographically and published in the reference book Biology and Culture of Channel Catfish. By following management recommendations resulting from this research, commercial catfish producers can realize up to a 30% increase in annual fry production.
Hydrogen Peroxide Use for Fungal Infections of Catfish Eggs
Fungal diseases of channel catfish eggs in commercial hatcheries can be a serious problem. Infected eggs are often treated with formalin. Although formalin is an effective therapeutic, concerns of safety exist amongst users. Hydrogen peroxide (H2O2) is an attractive environmentally friendly alternative for use as an external microbicide for fish and fish eggs. Several trials were conducted to evaluate the effect of H2O2 treatment on channel catfish hatching success when administered as bath or flow-through treatments and across a range of temperatures. The data collected during thesestudies was provided to the FDA as supplemental data in support a label claim for H2O2 use in treating fish eggs. By following the treatment recommendations, catfish producers have an effective alternative to formalin and can realize up to a 44% increase in annual fry production.
Effects of Feed Restriction on Catfish Endocrine Function
Farmed fish are sometimes subjected to periods of restricted feeding and fasting as a means of managing poor water quality and disease outbreaks; however, restricted feeding negatively affects fish growth. In an effort to define the physiological mechanisms involved, several studies were conducted to examine the effects of fasting on the somatotropic and corticotropic axes, both involved in energy partitioning. This research illustrates the importance of feeding status on fish endocrine systems involved in energy partitioning, and suggests a need for alternative practices to manage poor water quality and diseases on commercial fish farms to avoid negative effects on commercially desirable traits.
Catfish Growth Hormone Regulation
Growth hormone (GH) is an important regulator of growth in vertebrates; however, the mechanisms controlling the actions of GH in catfish were poorly characterized. This research characterized catfish genes coding for three putative GH-releasing peptide hormones (PACAP, GHRH, and ghrelin), growth hormone receptor (GHR), and ghrelin receptor (GHSR) and was the first to report the effects of cortisol on GHR mRNA expression in a fish. As such, it has advanced knowledge of growth hormone regulation in fish and the molecular evolution of the GHRH and GHSR genes.
Sedatives and Catfish Stress
Channel catfish handling, harvesting, and transport can cause elevated levels of plasma stress factors, such as cortisol, glucose, and lactate, known to affect disease resistance and fillet quality. This research evaluated the sedative efficacy of AQUI-S and metomidate hydrochloride for channel catfish, as well as the potential effects of these drugs on plasma cortisol, glucose, and lactate during handling and under conditions common to catfish harvesting and transport. Both AQUI-S and metomidate hydrochloride were found to be efficacious sedatives for channel catfish. Metomidate hydrochloride completely blocked cortisol release into the blood. AQUI-S significantly suppressed cortisol release and reduced plasma lactate concentrations during periods of low water oxygen.
Catfish Hormone Assay Development
The measurement of circulating hormones in channel catfish is critical to the characterization of economically important traits such as growth, stress tolerance, and reproduction. Furthermore, the use of radioisotopes in immunoassays presents safety and storage concerns and can be costly. Non-radioisotopic assays for the measurement of circulating concentrations of the channel catfish hormones cortisol, IGF-I and GH were developed and validated. The protocols developed in these studies reduce assay costs by as much as 70%, do not have any associated radiation safety concerns, and are essential to the efficient characterization of the physiological control of economically important traits in channel catfish.
Effects of Selective Breeding on Nutrient Efficiency
The NWAC103 line of channel catfish was developed and evaluated at the USDA-ARS Catfish Genetics Research Unit and jointly released to commercial producers in 2001 and 2002 in cooperation with the Mississippi Agricultural and Forestry Experiment Station. The germplasm release was primarily based on a 10-20% improvement in growth of the NWAC103 catfish relative to the industry average. This research assessed whether improvements in nutrient efficiency had also been made in the NWAC103 line and to determined whether further selection resulted in additional growth and efficiency improvements. It was demonstrated for the first time that nitrogen retention is negatively impacted by selection for faster growth rates in the NWAC103 line, but that further improvements in growth rate can be made through selective breeding.
Catfish Stress Physiology
Periods of stress in farm-raised catfish are often associated with disease outbreaks, poor growth, and diminished reproductive capacity. It is typically assumed that cortisol, as the primary stress hormone in fish, is the causative factor for these stress-related reductions in performance and fitness. Experiments were conducted to assess the roles of stress and cortisol in immune function, growth, reproduction, and fillet quality. In several instances, beneficial roles for cortisol were observed when severe or chronic stress had negative impacts on the observed trait. This research begins to define the roles of cortisol separate from stress in fish and may lead to the development of new uses for cortisol, such as enhancing reproduction, or to the discovery of other factors involved in the negative aspects of fish stress.
Striped Bass Ideal Protein
Feed costs represent 40-50% of farmed fish production costs. Thus, defining the dietary essential amino acid requirements of farmed fish is of major economic importance since protein is the most costly portion of feeds. Using traditional dose-response experiments to determine each of the ten individual essential amino acid requirements involves a substantial commitment of time and resources. This research adapted the “ideal protein” concept used by swine nutritionists to rapidly estimate all ten dietary amino acid requirements of the striped bass, conducting a thorough validation of the methodology through several experiments. As a result, the optimal dietary amino acid profile for striped bass was determined and a lysine requirement significantly higher than that being fed was established.
Striped Bass Plant Feedstuff Utilization
Utilization of plant feedstuffs in fish feeds provides a cost-effective means of reducing the dependence on fish meal as a dietary protein and energy source. However, poor nutrient availability associated with plant feedstuffs, and lowcarbohydrate tolerance by some fish species can create great difficulties when formulating least-cost feeds. These studies determined the availability of amino acids in plant-based feedstuffs compared to high quality fish meal, and the ability of striped bass to tolerate carbohydrate. As a result, it was determined that both soybean meal and corn gluten meal are suitable substitutes for fish meal in striped bass feeds, and that striped bass are able to tolerate carbohydrate, regardless of complexity, at levels less than 20% of the diet.