John A. Collier

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.

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.

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.

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.

Channel Catfish Production with Combination and Replacement Stocking

Abstract A production strategy for channel catfish Ictalurus punctatus that helps increase pond production, keeps size-classes of fish in discrete groups, and provides multiple harvest dates throughout the year was developed and tested. Fingerling catfish were graded into three different size-groups and stocked into 0.04-ha ponds at a density of 900 fish/pond (450 fish stocked loose in the pond and 450 fish stocked in a 1.25-m3 cage). The caged fish were either harvested for the whole-fish market (weight, 90–330 g) or transferred into vacated ponds when the daily feeding rate of the total pond (open pond and cage) reached 112 kg/ha. The remaining fish were fed until the daily feeding rate again reached 112 kg/ha; the fish in the open pond were then harvested for the fillet market (510–850 g). As a result of the combination stocking (fish stocked both loose in a pond and in a cage within the same pond) and the separation of size-cohorts, fish were harvested six times over an approximately 14-month period. ...