David E. Brune

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.

Filtration of green algae and cyanobacteria by Nile tilapia, Oreochromis niloticus, in the Partitioned Aquaculture System

Abstract Nile tilapia, Oreochromis niloticus , held in a timed pulse fed Continuous Stirred Tank Reactor (CSTR) were provided Partitioned Aquaculture System (PAS) algal-rich water dominated by green algae (i.e., Scenedesmus and Ankistrodesmus ) and cyanobacteria (i.e., Microcystis and Merismopedia ) to determine filtration rates (FR). A similar number and size of tilapias were stocked at 1.5 kg/tank into each of the six CSTRs (127 l) for 58-h experiment period. The cell counts of phytoplankton in water filtered by tilapias indicated significant reduction in green algae and cyanobacteria. Nile tilapia was more effective filtering the larger particle size taxa in both water sources. FR measured as mg of particulate organic carbon (POC) per kg wet fish weight per hour increased as POC increased. A curvilinear filter-feeding rate model provided a maximum filtration rate (FR max ) of 641 mgC/kg/h at 26 mgC/l in green algal-dominated water. The projected FR max of cyanobacterial-dominated water was 865 mgC/kg/h at 59 mgC/l. The derived filter-feeding rate models will help to describe Nile tilapia filtration kinetics in the PAS and the potential for control of nuisance cyanobacteria.

The partitioned aquaculture system: impact of design and environmental parameters on algal productivity and photosynthetic oxygen production

Abstract Fish production in pond culture systems is often limited by the dissolved oxygen (DO) concentration. Algal productivity greatly impacts the DO concentration but is difficult to control in traditional pond systems. The partitioned aquaculture system (PAS) was designed to increase fish production in pond systems by increasing net oxygen production through management of algal productivity and biomass concentration. This initial research was conducted to establish algal productivity and biomass levels in the PAS as a function of algal cell retention time, nutrient addition rate, water depth, and mixing and to characterize the photosynthetic oxygen production rate as a function of solar radiation. In order to focus on algal productivity, an inorganically fertilized PAS without fish was operated for this study. Algal productivity in the PAS was greater for the cell retention time of 1.2 days than 2.5 days, greater for external inorganic carbon addition rates of 0.6 and 1.2 mmol/l per day than for 0 mmol/l per day addition rate, greater for the water depth of 34 cm than 66 cm, and greater for the water velocity of 12.5 cm/s than 3.1 and 6.2 cm/s. Algal productivity rates of 5–10 g C/m 2 per day were achieved. Algal culture composition was impacted by inorganic carbon addition. Over a 2-year period, the algal culture was composed primarily of blue–green algae (Cyanophyta) when no external inorganic carbon was added, and green algae (Chlorophyta) at external inorganic carbon addition rates of 0.6 and 1.2 mmol/l per day. The maximum gross photosynthetic oxygen production rate at 20°C was found to be 0.096 mg O 2 /mg TSS per hour for predominantly blue–green algal cultures and 0.14 mg O 2 /mg TSS per hour for green algal cultures. Corresponding maximum algal specific growth rates, calculated using a literature value for algal cell composition, were 0.077 and 0.12/h for blue–green and green algae, respectively.

Comparative Nile tilapia and silver carp filtration rates of Partitioned Aquaculture System Phytoplankton

Abstract Nile tilapia ( Oreochromis niloticus ) and silver carp ( Hypophthalmichthys molitrix ) held in timed-pulse feeding chambers were provided water dominated either by green algae ( Scenedesmus , Ankistrodesmus and Tetraedron ) or by cyanobacteria ( Microcystis ) to compare filtration rates (FRs). FRs were expressed as suspended particulate organic carbon (POC)/kg wet fish weight/h and as phytoplankton units filtered based on counts. Nile tilapia and silver carp filtration significantly reduced phytoplankton number of both taxonomic groups with the larger phytoplankton being filtered proportionally more than the smaller phytoplankton. Nile tilapia FR of green algae was significantly higher than silver carp; however, silver carp FR of cyanobacteria was higher than Nile tilapia. Ivlevs 90% saturation FRs (FR 90 ) in green-algal and cyanobacterial water sources were 702 and 812 mgC/kg/h for Nile tilapia and 414 and 1028 mgC/kg/h for silver carp, respectively. Silver carp were observed to reach these FR 90 values at lower POC concentrations than Nile tilapia with both green algae and cyanobacteria.

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.

Transport limitation of oxygen in shrimp culture ponds

Abstract A 120-acre shrimp farm located in southeast Texas has failed for three years to produce expected yields of shrimp despite intensive management. Data obtained from these ponds are combined with observations from other culture facilities to support the hypothesis that the degree of mixing of pond water is the primary limitation to oxygenation of the benthic biomass in a shrimp culture pond. The implication of this conclusion is that shrimp ponds are advection limited; therefore, rational design of such facilities will require detailed data concerning the impact of interactions of pond size, depth and geometry with wind speed, and aerator placement, upon pond mixing.

Profitability comparison of the partitioned aquaculture system with traditional catfish farms

Abstract The Partitioned Aquaculture System (PAS) provides a promising intensive aquaculture technology that is efficient and profitable, while simultaneously solving a variety of culture problems. This creates a sustainable aquaculture technology, which is environmentally safe and economically feasible. The PAS eliminates water discharge and reduces land usage and ground water requirements. The PAS system production process was modeled for catfish production using a growth model developed from observed data. The results of the PAS economic analysis were compared with two traditional catfish production scenarios. Comparisons were made between estimated investment requirements, operating costs and internal rates of return and breakeven points for alternate production systems and land ownership status. The results look promising, but research is ongoing on how best to manage the filter feeder component of the PAS.

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.