Thomas E. Schwedler

Intensification of pond aquaculture and high rate photosynthetic systems

Abstract Aquaculture production systems may range from tanks and raceways, in which water quality is controlled by water dilution and discharge to the environment to captive water systems, in which water quality is controlled by microbial reactions within the tank or pond. Attempts at intensification of pond aquaculture beyond the commonplace practice of supplemental aeration may be classified into categories of physical/chemical techniques and a broad range of microbial techniques. Most of these techniques are directed at raising the ‘ceiling’ of the system ammonia detoxification rate. Physical–chemical techniques for intensification of pond aquaculture have included use of in-pond cages and raceways, water blending and shading of the algal community, as well as, direct flocculation and removal of algal and bacteria biomass from ponds. A variety of microbial processes can be used to reduce ammonia levels in a conventional pond. These processes include nitrification/denitrification, photosynthesis, and heterotrophic bacterial re-growth. In this paper, simplified microbial growth fundamentals, and elemental mass balances are used to analyze and compare the various aquaculture intensification techniques and, in particular, to compare conventional and heterotrophic techniques to the use of high rate photosynthetic systems. Direct or indirect photosynthetic systems include enhanced algal systems (with water mixing), polyculture, hydroponics, wetlands, and terrestrial irrigation/fertilization. The development of Clemson Universitys Partitioned Aquaculture System (PAS) constitutes an attempt to combine a number of the various physical, chemical, and microbial intensification techniques into a single integrated system. The PAS represents an adaptation of high rate microalgal culture to produce a sustainable, minimal discharge, high yield, and more controllable fish production process. The PAS combines the advantages of process control of recirculating tank aquaculture with the lower costs of earthen pond aquaculture. Central to the economic success of the PAS is the use of low speed (1–3 r.p.m.) paddlewheels as an energy efficient means of establishing a uniform water velocity field within an aquaculture pond. The PAS represents a redesign of the conventional aquaculture pond culture technology providing a spectrum of applications ranging from moderate yield (6700–11 200 kg/ha) ‘engineered ecosystems’ to high yield (16 800–33 600 kg/ha) controlled ‘production processes’. This high rate photosynthetic system offers the potential for a 90% reduction in total water usage per unit of fish produced. The modular nature of the PAS, the increased productivity per unit area, reduced water requirement, and reduced environmental impact offers the potential for fish culture systems to be installed at sites not currently suitable for conventional aquaculture.

Effect of Vitamin E on the Immune Response of Channel Catfish to Edwardsiella ictaluri

Abstract Three-month-old fingerling channel catfish Ictalurus punctatus were fed purified diets supplemented with ∝-tocopherol acetate to provide 0, 60, and 2,500 mg vitamin E/kg for 180 d. A 30-s immersion bath and an oral booster were used to deliver a bacterin of formalin-killed Edwardsiella ictaluri to half of the fish from each dietary treatment. Resistance of red blood cells to peroxidation was used as an index of antioxidant status. The susceptibility of red blood cells to oxidative hemolysis decreased with increasing levels of dietary vitamin E. Vaccinated and nonvaccinated fish were evaluated for agglutinating antibody titers and macrophage activity. Humoral antibody titers in response to E. ictaluri were significantly (P ≤ 0.05) higher in vaccinated fish than in nonvaccinated fish; however, no such differences in agglutinating antibody titers were detected among any of the dietary treatment groups. Both vaccination and vitamin E significantly enhanced the ability of macrophages to phagocytize vi...

Effects of Stress on Susceptibility of Naive Channel Catfish in Immersion Challenge with Edwardsiella ictaluri

Abstract The effects of stress on the susceptibility of fingerlings of channel catfish Ictalurus punctatus to Edwardsiella ictaluri during immersion challenges were evaluated. Channel catfish fingerlings were exposed to a standardized confinement stressor for 30 min. Infections were established in stressed and nonstressed channel catfish fingerlings by exposure to E. ictaluri under aerated static conditions for 24 or 48 h. Stress and increased time of static bacterial exposure significantly decreased the survival of channel catfish fingerlings after immersion challenge. This study established a relationship between a behavioral stressor (confinement) and increased susceptibility of channel catfish to E. ictaluri infection. From estimates ofexperimental error, a relationship between the precision of the challenge system and the number of replicate aquaria per treatment was established. This analysis indicated that the immersion challenge is associated with a high degree of variability, which limits the eff...

15 Health management

Publisher Summary Channel catfish health management begins with creating and maintaining a proper living environment for the fish. Good management also includes the design and operation of a production facility that minimizes the impact of stress on the fish. To promote health and minimize stress, fish should be provided with their basic needs: sufficient space, good water quality, a nutritionally complete diet, limited physical disturbance, protection from predators, and prudent handling. Once these needs are met, it is important to limit contact with disease-causing agents and to prevent environmental deterioration. Even in well-designed and properly managed facilities, it is not uncommon for diseases to occur. Once a disease outbreak ensues, effective health management requires three basic steps: problem identification, diagnosis, and corrective management—all of which must be performed in a timely manner to avoid further losses. Whenever multiple factors contribute to the disease process, it makes the diagnosis more difficult and often complicates corrective management. Many fish health problems, such as oxygen depletions, can be recognized and corrected by the fish culturist on the pond bank. This chapter discusses factors affecting the disease process in catfish and steps that can be taken to diagnose disease problems. The chapter provides an overview of the various options for managing infectious diseases. Several specific management procedures for the important catfish diseases are also discussed.

19 Partitioned aquaculture systems

Publisher Summary Low capital cost and the relative reliability offish production are the major advantages offish culture in earthen ponds. Disadvantages of pond production are the need for continuous management of dissolved oxygen concentrations, as well as other fluctuating water quality variables. Labor requirements (especially for harvesting) and problems with off-flavors, predators, and diseases represent additional management difficulties. These issues, combined with land, water, and environmental resource constraints, have stimulated a search for technological improvements in aquaculture practices. Shifting production to more energy-intensive systems is one solution, either through application of increased aeration (2 to 38 kW/ha; 1 to 20 hp/acre) in ponds, or by abandoning the land-intensive pond altogether and shifting production to higher density recirculating tank or raceway systems. Researchers and producers have made significant efforts to address the need for intensification of pond aquaculture while minimizing environmental impacts. Pond aquaculture productivity is limited first by oxygenation of the water column and second by accumulation of ammonia to levels toxic to the cultured organisms.

Extracellular Products Associated with Virulent and Avirulent Strains of Edwardsiella ictaluri from Channel Catfish

Abstract Little is known about the pathogenic mechanisms possessed by Edwardsiella ictaluri, the etiological agent of enteric septicemia of catfish (ESC). Extracellular products probably play a major role in the pathogenesis of the disease. Comparative studies were done to assess the extracellular products present in virulent and in avirulent (attenuated) strains of E. ictaluri. Virulence factors studied were capsule production, detection of surface proteins, and hemolytic and chondroitinase activities. Electron microscopy showed a fibrilar network connecting virulent cells. Virulent isolates had greater amounts of capsular material and surface proteins, and they demonstrated a greater ability to degrade chondroitin than avirulent forms. There was no clear correlation between hemolytic activity and virulence.

Variability of Harvest Sizes of Channel Catfish as Related to Stocking-Size Variability

Abstract Variation in total length for a population of channel catfish (Ictalurus punctatus) was evaluated by marking fish of discrete sizes within the population at stocking. At harvest, the variation of the overall population and of the marked fish was determined. Marked channel catfish subpopulations maintained their size ranking and had reduced variability relative to the overall population (SDs, 2.07–2.15 for the marked groups versus 2.82 for the total population). The coefficient of variation (100 × SD/mean) for the total population declined from 12.4% at stocking to 8.8% at harvest; coefficients of variation for the marked groups were 6.2–7.3% at harvest. Apparently, variability at harvest is due to both stocking variability and differential growth rates.

Effects of the Immunomodulator Ecteinascidia turbinata Extract on Edwardsiella ictaluri Infection of Channel Catfish

Abstract Ecteinascidia turbinate extract (Ete) dramatically decreased the survival of channel catfish Ictalurus punctatus that were challenged with a virulent strain of Edwardsiella ictaluri. A 0.625-μg or a 1.250-μg dose of Ete administered intraperitoneally 2 d before, on the same day, or 2 d after a 14-d LD50 dose (dose lethal to 50% of the test fish) of E. ictaluri decreased survival to 20% or less after 14 d. The extract significantly (P = 0.05) enhanced, by approximately 2.5-fold, the ability of adherent anterior kidney cells to phagocytize. However, Ete did not significantly affect antibody titers to E. ictaluri compared to those of control fish not treated with Ete. This study demonstrated that although immunoenhancement occurred in channel catfish injected with Ete, their ability to survive infection with E. ictaluri decreased.

Growth Response of Fingerling Channel Catfish to Sheltered Feeding

Abstract A fish excluder that provided a sheltered feeding area for small fingerling channel catfish (Ictalurus punctatus) in a multiple-cohort production system was tested. Small fingerlings (mean weight, 12.7 g) were stocked in ponds with larger submarketable fish (286 g). Fingerlings in the ponds with excluders showed a 64% increase in weight gain over fish in the control group.

Production Characteristics of Channel Catfish, Ictalurus punctatusStocked at Two Densities in the Partitioned Aquaculture System

Abstract This study was conducted to determine if channel catfish could be cultured at an increased density in the Partitioned Aquaculture System (PAS) without significantly affecting performance. Channel catfish fingerlings (36.53±6.76 g; mean ±SD) were initially stocked into six 9.15 m3 sections at 3,461±317 fish per section, twice the designed carrying capacity, and fed twice daily to satiation. After 75 days, the density of three units was reduced by approximately 50% and all six units were fed for another 97 days. There was no significant difference (P > 0.05) in mean growth rate, feed conversion ratio, or production between fish grown at the low- and high-density treatments. Also, length variation (CV) and condition factors (K) were similar (P > 0.05) between fish grown at the low and high-density. Increasing density by twice the designed carrying capacity did not affect performance of channel catfish in the PAS.