Recipient Organization
MISSISSIPPI STATE UNIV
(N/A)
MISSISSIPPI STATE,MS 39762
Performing Department
FWRC-Wildlife,Fisheries&Aquacu
Non Technical Summary
Agricultural productivity depends on animal health, and animal health depends on maintenance of physiological homeostasis and resilience to change. In the US catfish industry, physiological homeostasis relates closely to environmental conditions, as catfish are ectothermic. Seasonal, weekly or rapid changes in environmental conditions have direct impacts on the physiological state of fish, impacting feed intake, metabolic rate, energy stores, gas exchange, stress and disease resistance. Similarly, handling practices involved in culture, harvest and transport also induce stress and perturbations in homeostasis potentially increasing disease susceptibility. Physiological departures from homeostasis may also relate to product quality or fillet quality for the consumer. Understanding of the links between environment, handling and physiological homeostasis are limited in the catfish industry, and particularly for hybrid catfish, a cross between a female channel catfish (Ictalurus punctatus) with a male blue catfish (I. furcatus), which now approach 50% of production. This information is necessary for industry adaptation to environmental change, improvement of harvest practices and adoption of more intensive culture practices.Fish, like many other aquatic organisms, are ectothermic and constrained by environmental conditions. A basic understanding of aerobic metabolic capacity and the influence of environmental conditions on this capacity is extremely important for guiding culture practices. Research under this project will examine the adaptive capacity of channel and hybrid catfish under a range of environmental conditions. Experiments will also help to understand how oxygen, carbon dioxide and pH influenceinternal handling of oxygen and aerobic metabolic capacity. In addition, minimum thresholds of environmental oxygen and carbon dioxide will be determined via internal regulatory ability of the blood.This researchwill be important for improving industry resilience to environmental change, improving culture, handling and harvest practices, and guiding research on disease recovery. Studying the impacts of environmental and culture stress on metabolic capacity is important forimprovingculture performance and efficiency.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
The long-term goal of the research program is to understand catfish capacity for adaptation to perturbations in homeostasis, particularly related to stress response mobilization and metabolic energy use. The overall objective of this application, which is the next step in the long-term goal, is to address environmental influences on homeostasis, metabolism and disease resistance through analysis of gas handling within the blood. The central hypothesis is that homeostatic maintenance of blood oxygen levels directly relate to resilience to environmental change and infection. Our research has already established important leads in these areas in collaboration with catfish producers and processors, and will be carried out at a facility well-located within the heart of the catfish industry.This proposal will address the following specific objectives through securing a keystone instrument that will facilitate these studies, a complete blood-gas system specifically developed for use with ectotherms:Quantify adaptive capacity of channel and hybrid catfish for oxygen delivery and carbon dioxide removal following acclimation to, or acute exposure to a range of temperature and oxygen conditions. Our working hypothesis is catfish are constrained more by oxygen than temperature, but both have interactive effects particularly at high temperatures, with hybrid catfish having a slightly greater adaptive capacity than channel catfish.Determine constraints of carbon dioxide on catfish blood-gas dissociation with application to intensive culture practices. Our working hypothesis is catfish have a high capacity for oxygen delivery and carbon dioxide waste removal to tissues even at high external carbon dioxide concentrations, but that temperature and hypoxia greatly impact this capacity.Determine minimum levels of external oxygen tension (pO2) to maintain circulating pO2, and compare with different states of disease in channel and hybrid catfish. Our working hypothesis is a threshold exists between external and internal pO2, whereby once a lower limit is crossed, internal pO2 falls rapidly. Further, disease is debilitating in part due to reductions in this threshold from impacts on red blood cells.
Project Methods
The specific objectives of this proposal will be facilitated by the purchase of a complete blood gas system manufactured by Loligo Systems, Denmark. This instrument is designed for use with ectothermic organisms such as catfish. Associated equipment will include a desktop computer to run the software associated with the instrument. The instrument requires only small volumes of blood, allows modification of blood gases, including both pO2 and pCO2, and manipulation of temperature and pH. These capabilities are necessary for assessing adaptive capabilities for oxygen exchange and fueling aerobic metabolism, waste removal and pH balance. This instrument facilitates determination of oxygen equilibrium curves under a variety of environmental and physiological conditions, mimicking different states of blood oxygenation and evaluating capacity for tissue delivery of oxygen and carbon dioxide uptake by red blood cells.This instrument will be used to address objectives examining the central hypothesis that homeostatic maintenance of blood oxygen levels directly relates to resilience to environmental change and surviving infection.For the first objective, the first experiment will acclimate channel and hybrid catfish to a range of environmental temperatures from winter conditions to extreme summer conditions. Acclimation temperatures will consist of 10, 18, 26, and 34°C, where fish will be held for 2-3 weeks. Fish will be maintained in large (4,000-L) temperature controlled recirculating systems at the Mississippi State University South Farm Aquaculture Facility. Blood samples will be collected from 6 fish per temperature. Oxygen dissociation curves will be generated from collected blood and compared between temperature treatments. Results will be compared with energy substrate levels that impact oxygen dissociation such as nucleoside triphosphates using commercial measurement kits (Sigma Aldrich).For the first objective, the second experiment will examine chronic and short-term exposures to hypoxia in channel and hybrid catfish. Hypoxia exposure levels will follow previous research in our laboratory (Aboagye and Allen 2014; Ciaramella 2015), with severe, moderate and mild levels of hypoxia contrasted with air-saturated water (normoxia). In addition, hyperoxic conditions will also be evaluated, similar to conditions in hauling tanks. Catfish will be acclimated to the conditions for 1 week prior to collection of blood samples for chronic exposure and 8 hours for acute exposure. Conditions will be relevant to daily cycles of hypoxia in ponds or chronic conditions which may occur due to low oxygen availability and high density.For the second objective, channel and hybrid catfish will be exposed to three levels of carbon dioxide concentrations for either a short-term (4-h) or a long-term (72-h) period using natural addition of carbon dioxide from fish and carbon dioxide gas following previous experiments in our laboratory (Allred et al. unpublished data). The ability of blood to deliver oxygen to tissues in high carbon dioxide conditions will be contrasted with low saturation levels, allowing for examination of a range of physiological operation under potential culture conditions. Abilities will further be evaluated at moderate and high temperatures (24 and 34°C) and normoxic and hypoxic conditions.For the third objective, the first experiment will manipulate external pO2 and measure internal pO2 in cannulated catfish subjected to a range of temperature, oxygen and carbon dioxide conditions. Techniques for cannulation are established in our laboratory (Allen et al. 2009), and can be used to sequentially sample blood from fish with minimal additional handling stress. Fish will be examined at a resting state and with mild exercise using a swim flume following previous techniques in our laboratory (Aboagye and Allen 2014) to understand relationships with available energy.For the third objective andthe second experiment, blood oxygen dissociation curves at different levels of hypoxia established under Objective 1 will be compared with healthy and diseased catfish. Diseased catfish will be sampled collaboratively on commercial farms following previous techniques (Allen et al. 2015), and for the first experiment will include moderately anemic catfish and severely anemic catfish. Results will be contrasted with blood dissociation capability in healthy fish exposed to hypoxia. Future experiments will examine relationships with Aeromonas and trematode infections using on-campus facilities for exposure.