Aquacultural Engineering 34 (2006) 157–162 www.elsevier.com/locate/aqua-online
Design criteria for recirculating, marine ornamental production systems Craig A. Watson *, Jeffrey E. Hill Tropical Aquaculture Laboratory, Department of Fisheries and Aquatic Sciences, University of Florida, 1408 24th Street SE, Ruskin, FL 33570, USA
Abstract While recirculating aquaculture systems for food animals are well defined in the literature, little information is available for the emerging production of high value marine ornamental species. These organisms typically require systems which operate within a narrow range of parameters compared to most food animals, and in addition to growth and survival issues, individual appearance of animals is critical to success. This paper is a general review of the primary design criteria parameters for the production of marine ornamental species in stable, oligotrophic, recirculating aquaculture systems. # 2005 Elsevier B.V. All rights reserved. Keywords: Marine ornamentals; Recirculating systems
1. Introduction Recirculating water systems are well established in aquaculture. Professional engineers, research scientists, and aquaculturalists have succeeded in creating closed systems capable of performing essential mechanical, chemical, and biological processes to insure health and survival of numerous, commercial aquaculture products. Successful systems must rely heavily on initial design criteria being suitable for the cultured organism, while also taking into account costs associated with construction and operation. Most * Corresponding author. Tel.: +1 813 671 5230; fax: +1 813 671 5234. E-mail addresses:
[email protected] (C.A. Watson),
[email protected] (J.E. Hill).
systems are designed to maximize production of the target organism, in a minimum amount of space, with the least amount of cost. In addition, the appearance (e.g., color) and condition of individual cultured organisms is a primary concern due to the nature of the market (i.e., ornamental). Major components of any system include growth units (i.e., tanks, aquaria), solids removal, biological filtration, aeration, water delivery (i.e., pumps, air lifts), and often a form of sterilization (i.e., UV, ozone). Marine ornamental aquaculture is rapidly becoming an economically viable enterprise, and a subject of interest to the environmental and research community. In Florida, a very well developed ornamental aquaculture industry exists, focused primarily on freshwater species, but also involving an increasing number of marine tropical species. Aquaculture in
0144-8609/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaeng.2005.07.002
158
C.A. Watson, J.E. Hill / Aquacultural Engineering 34 (2006) 157–162
Florida exceeded US$ 95.5 million in 2003, with ornamental aquaculture of fish making up 49.4% of the total (US$ 47.2 million) in 2003 (FASS, 2004). However, only a minor fraction of the total value was derived from marine ornamental sales. Relatively small, but growing, marine ornamental industries are found in other states. Land cost, building regulations, and environmental permitting often prohibit sitting of facilities in coastal locales where flow-through systems could be used, so there is growing interest in utilizing inland, closed-system production for marine ornamental species. Marine ornamental species present their own design criteria which must be considered when developing such systems. Unfortunately, there is relatively little published research in this field and much of the available information is found in the gray literature or is anecdotal.
2. Design criteria variables As in any design process for aquaculture, the species in culture is key to determining system criteria. Currently there are several dozen species of fish, numerous hard and soft coral species, several macroalgae species, and perhaps one dozen species of ornamental mollusks in culture. All of these species originate from tropical reef ecosystems, which are considered oligotrophic and highly stable. Due to the economic value of all ornamental species, but especially marine species, maximization of production (kg/unit space), is often not as critical as maintaining suitable water quality and other environmental conditions to insure survival, attractive appearance, and reproductive success. Because marine ornamentals have evolved in a tropical reef ecosystem, their tolerance for change and marginal conditions is not as high as many food species (e.g., tilapia). Therefore, design criteria for marine ornamentals should focus on maintaining a stable and narrowly defined set of criteria. 2.1. Light Many of the ornamental marine invertebrate species rely heavily on zooxanthellae – symbiotic algae which grow in their tissues – to perform photosynthesis, and thereby provide nutrition to the animal. Corals (soft and
hard corals), Tridacna clams, and many anemones, require healthy zooxanthellae for optimum performance. Coral bleaching occurs when these zooxanthellae are expelled from the tissues. In addition to compromising the health of the host organism, as an ornamental, the individual or colony may no longer be ‘‘attractive’’ if the zooxanthellae are in poor condition or absent. Being ornamentals, appearance is a primary consideration and poor color can decrease sale price. While high water temperature is the suspected causative agent in coral bleaching in the oceans (Hoegh and Smith, 1989), improper lighting can cause suboptimal performance of the zooxanthellae (Kinzie et al., 1984; Kinzie and Hunter, 1987). The most common cause of problems with zooxanthellae in captivity is improper lighting— inadequate intensity or the wrong spectrum. The marine reef aquarium industry has developed a wide selection of lighting systems which have proven effective in maintaining zooxanthellae in corals and other invertebrates for the hobbyist and public aquaria. Very high output (VHO) fluorescent lights are available in a wide variety of spectrums, from full spectrum to actinic blue. Metal halide lamps are perhaps the standard choice, because they produce a wide spectrum and have a high output from a small source. Sodium vapor bulbs also have been shown to support zooxanthellae, are less expensive than metal halides, but do not produce as broad a spectrum of light as metal halide bulbs (a concern in display systems). Sunlight, a natural, full spectrum source, is of course the preferred option. Too much light can also affect the appearance of ornamentals. In many species, the animal may ‘‘darken’’ or become ‘‘brownish’’ as UV protecting pigmentation is increased in the tissue of the host animal when too much light is provided. Excessive light intensity also may lead to bleaching (Hoegh and Smith, 1989). Most ornamental invertebrate species are found in water from 10 to 20 m in depth, where light penetrates, but is highly filtered by the water above. Corals, anemones, and other invertebrates which utilize zooxanthellae are almost always more colorful when found at these depths, as opposed to those in the shallow reef zone. In Florida greenhouses, preliminary data suggest that a 50% shade cloth will provide adequate lighting for healthy zooxanthellae, while not over stimulating pigmentation of the tissue in many
C.A. Watson, J.E. Hill / Aquacultural Engineering 34 (2006) 157–162
invertebrates, but much research is still needed to determine the optimal lighting criteria for given species. In addition to affecting the pigmentation of ornamental species, too much light also increases the occurrence of nuisance algae, especially filamentous green algae, and may make temperature control more difficult.
159
not grow properly unless they are constantly submitted to a periodic and significant surge, similar to wave action on the reef. A simple surge device can be constructed utilizing the same principle as a pipette washer (i.e., ‘‘Carlson’’ surge device; Fig. 1). Branching corals grown in absence of this surge action will grow vertically and with thin, brittle branches.
2.2. Water movement 2.3. Water quality Water movement should be considered for each species being cultured. Water movement is often accomplished using air-lifts, air stones, or water returns from filters or degassing devices (e.g., Loyless and Malone, 1998). Some species, especially in the fish group, may perform poorly (e.g., slow growth) if the water movement is too strong, especially during breeding. For sessile invertebrates, water movement influences hydromechanical boundary layers of water which, in turn, affect the flushing and deposition of sediments and the diffusion of solutes (e.g., oxygen, Ca2+) (Dennison and Branes, 1988; Shashar et al., 1996). Species such as the branching, hard corals will
As stated, the evolution of marine ornamentals has occurred in tropical reef ecosystems, where conditions are relatively stable throughout the year. The initial design of a system should allow for easy monitoring and maintenance of water quality. There are several key parameters and design criteria which deserve attention. 2.4. Salinity Synthetic sea salts are most commonly used, but require at least 24 h of mixing, so a separate container large enough to hold the volume of any anticipated
Fig. 1. Simple ‘‘Carlson’’ surge device.
160
C.A. Watson, J.E. Hill / Aquacultural Engineering 34 (2006) 157–162
water replacement should be incorporated in the design. This container should be well-aerated and have temperature control to insure the make-up water has been thoroughly mixed, is saturated with dissolved oxygen, and will not negatively impact the temperature of the system. Freshwater should also be available to adjust salinity increases caused by evaporation. As many ground water and municipal water sources may contain unacceptable amounts of dissolved elements, it is recommended that freshwater replacement water be from a tested source or be produced by reverse osmosis. Salinity for most marine ornamentals, especially tropical, coral reef, invertebrates should be maintained consistently between 33 and 35 ppt. 2.5. Other elements Although dominated by sodium chloride (30 ppt of 33 ppt total ‘‘salts’’), seawater contains at least 40 minerals and numerous dissolved gases, some of which are consumed by processes in a recirculating system (e.g., carbonates), and others which are taking up by animals (e.g., calcium, iodine, strontium) (e.g., Loyless and Malone, 1997; Reynaud et al., 2004). While much research remains to determine optimum levels and ratios for many of these elements, efforts should be made to mimic ratios found in open reef ecosystems. Design of the system should include a method for easy and precise addition of various elements whenever there levels fall below optimum. Calcium carbonate reactors are simple units where water moves slowly through a bed of finely crushed limestone, continuously adding carbonates to the system. Strontium, another important element in calcification, should be measured at least monthly, and added as need to achieve 13 mg/kg (ppm). 2.6. Temperature Reliable and adequate temperature control methods are essential to marine ornamental production, as many species are extremely intolerant of temperatures above or below the narrow ranges found on tropical reef ecosystems. Shallow water species are typically more tolerant, but as mentioned, most economically important species come from waters of 10–20 m in
depth. At these depths, most tropical reef systems are within a few degrees of 25 8C, on a year round basis. Maintaining a recirculating system at this range and within such narrow tolerances requires that initial design include heat pumps, chillers, heaters, or a combination of these to maintain temperature year round. In Florida, summer temperatures require cooling, and winter temperatures require heating. However, an increase in water temperatures may benefit reproduction in some species (e.g., 28–32 8C for the anemone fish Amphiprion sebae; Ignatius et al., 2001). 2.7. Nitrogen Most marine ornamental species have a very low tolerance for ammonia or nitrite when compared to freshwater species. Nitrate toxicity is also a concern at levels which would have little to no impact on freshwater species. For example, in the anemonefish Amphiprion ocellaris, high nitrate levels (i.e., 100 mg/ l) reduced growth of juveniles and delayed metamorphosis of larvae with subsequent declines in growth and survival (Frankes and Hoff, 1982) Invertebrates such as corals may be especially affected. For example, rates of skeleton building declined by up to 50% in corals exposed to 20 mM of nitrate (Marubini and Davies, 1996). Nitrogen is the limiting nutrient in most marine systems, and as such presents a challenge for design criteria. Even moderate levels of nitrogenous wastes can result in significant, nuisance algae blooms in the system. Biological filtration must be able to maintain total ammonia nitrogen (TAN) and nitrite, at levels near zero (<0.004 mg/l) for influent water. Nitrate should be maintained below 100 mg/l, and in nature occurs at levels less than 1 mg/l. High nitrates typically result in algal blooms and over time can result in a lowering of pH. Biological filtration should be designed and sized to effectively maintain nitrogenous wastes at levels approaching zero. Common and effective filters for the management of ammonia and nitrite include bead filters, drop bead filters, and fluidized bed sand filters (Westerman et al., 1996; Sastry et al., 1999). Use of algal scrubbers or anaerobic denitrifying chambers can be incorporated to remove nitrate, but most existing facilities use nitrate build-up as the primary trigger for performing water exchange.
C.A. Watson, J.E. Hill / Aquacultural Engineering 34 (2006) 157–162
161
2.8. Dissolved gases
2.10. Loading capacity/system size
Management of gas exchange is an important design criterion for marine ornamental systems. Maintaining high concentrations of dissolved oxygen is necessary for health of cultured organisms and proper functioning of biological filters (i.e., maintenance of aerobic bacteria). Because of the relatively low biomass of cultured organisms in most marine ornamental systems, aeration (e.g., air stones, air lifts, packed column) is generally sufficient for gas exchange. However, diffusion of oxygen from an oxygen generator or supply tank may be required in intensive culture situations. In general, dissolved oxygen levels should not fall below 5 mg/l. Stripping of carbon dioxide can be achieved by vigorous aeration from air stones or through de-gassing with a packed column.
When valued on a per weight basis, ornamental species are one of the highest valued aquaculture commodities. However, except for a few high-volume sales items (e.g., feeder guppies), the actual market is driven more by number of animals, not weight. Weight can be a useful tool in estimating production parameters such as feeding rates, oxygen demands, and nitrogenous waste production, but should be used cautiously when designing a production system and business plan. Individual rearing tanks are often small when compared to food aquaculture, especially for maintenance of brood stock. For example, in marine ornamental fish, current production is concentrated on species which develop strong pair bonds, and produce regular clutches of eggs, so breeding pairs are maintained separately in small aquaria (38 l). Although some species may require larger breeding tanks, the scale is more similar to home aquaria than to tank sizes common in other aquaculture industries. Likewise, grow out tanks are generally smaller than food production aquaculture, and may contain only hundreds of individuals. Actual stocking rates and holding capacity is often a fraction of what has been proven achievable in aquaculture, but is still economically feasible. Ornamental production in general is more similar to a fingerling than a food fish operation, with fish as young as 3 months being marketable. Invertebrate culture, perhaps the fastest growing segment of marine ornamental production, is not based on conventional loading capacities and feeding rates, but on horizontal space. Although volume and flow rate are important in assuring optimum water quality, limits to production are based primarily on how many animals can be placed in the given horizontal space.
2.9. Sterilization/biosecurity The high value of individual animals in a marine ornamental production facility demand close attention to disease management. While many species are readily available in the market, obtaining brood stock may be extremely difficult, especially for late maturing species (e.g., Pomecanthus spp., Tridacna clams). Commercial production also demands numerous tanks, and often several species of animals to secure a market, with each tank representing a separate population. Isolating these populations from each other is one of the most effective means to control a disease outbreak when it occurs. The two most common methods for sterilizing water in aquaculture are ozone and ultraviolet light. Ozone is highly reactive in seawater, and therefore effective as a sterilizing technique. However, there is concern over the production of ozone by-products, many of which we know little about. Because of this, UV sterilization is considered the preferred method for marine ornamental production. Initial design criteria for commercial marine ornamental production should also include a separate area, completely isolated from the production tanks, for quarantine of any new animals. Rigorous quarantine should be maintained for at least 1 month.
2.11. Water consumption Inland, indoor production of marine ornamentals demands that water be conserved. Most commercial operations utilize synthetic sea water mixes, which cost approximately US$ 0.02 l 1, so water exchange can become a major cost of production. In addition, many locales have strict environmental regulations on
162
C.A. Watson, J.E. Hill / Aquacultural Engineering 34 (2006) 157–162
the discharge of saline water at an inland location. Because of the cost and discharge restrictions, recirculating marine ornamental systems should be designed to minimize or eliminate the need for water exchange (e.g., Gelfand et al., 2003). Most water use is associated with solids removal (either siphoning or backwash water from filters), and water exchange to remove nitrate. Mechanical filtration which utilizes small amounts of water, such as drop bead filters, is preferable to those requiring a power backwash. Algae scrubbers (see Adey and Loveland, 1998), or simple incorporation of aquatic plants in the system (usually the sump), can also be used to remove nitrogen and other nutrients such as phosphorous. Incorporating plants as a nutrient sink can also add another product to the system, as many of the macroalgae are sold in the aquarium trade. Another path for water consumption which is often overlooked is in shipping water. When product is sold several gallons of water are used for each box, and in large operations this can amount to hundreds, if not thousands of gallons per week. Using system water that has been sterilized by ozone or UV is suitable, and actually may serve as the needed water replacement necessary to remove unwanted wastes, and replenish depleted elements and compounds.
3. Summary Marine ornamental aquaculture has become economically feasible, and much interest has been generated for inland, recirculating systems. Design criteria need to focus on creation of a stable, almost oligotrophic system which will closely mimic the conditions of a tropical reef system. The economics of marine ornamentals allow for incorporation of system components which may be infeasible for food aquaculture due to their costs, but caution is still advised to assure that production costs do not exceed sales value or greatly diminish profitability. Systems typically will incorporate numerous, relatively small tanks to house small fish and animals of several varieties, which make system design quite different from many food aquaculture systems.
References Adey, W.H., Loveland, K., 1998. Dynamic Aquaria: Building Living Ecosystems. Academic Press, San Diego, CA. Dennison, W.C., Branes, D.J., 1988. Effect of water motion on coral photosynthesis and calcification. J. Exp. Mar. Biol. Ecol. 115, 67–78. FASS, 2004. Florida Agricultural Statistics Service, Orlando, FL. http://www.nass.usda.gov/fl. Frankes, T., Hoff Jr., F.H., 1982. Effects of high nitrate nitrogen on the growth and survival of juvenile and larval anemonefish Amphiprion ocellaris. Aquaculture 29, 155–158. Gelfand, I., Barak, Y., Even-Chen, Z., Cytryn, E., Van Rijn, J., Krom, M.D., Neori, A., 2003. A novel zero discharge intensive seawater recirculating system for the culture of marine fish. J. World Aquac. Soc. 34, 344–358. Hoegh, G.O., Smith, G.J., 1989. The effect of sudden changes in temperature, light, and salinity on the population density and export of zooxanthellae from the reef corals Styophora postillata Esper and Seriatophora hystrix Dana. J. Exp. Mar. Biol. Ecol. 129, 279–304. Ignatius, B., Rathore, G., Jagadis, I., Kandasami, D., Victor, A.C.C., 2001. Spawning and larval rearing technique for tropical clown fish Amphiprion sebae under captive condition. J. Aquac. Trop. 16, 241–249. Kinzie III, R.A., Hunter, T., 1987. Effect of light quality on photosynthesis of the reef coral Montipora verrucosa. Mar. Biol. 94, 95–110. Kinzie III, R.A., Jokiel, P.L., York, R., 1984. Effects of light of altered spectral composition on coral zooxanthellae associations and on zooxanthellae in vitro. Mar. Biol. 78, 239–248. Loyless, J.C., Malone, R.F., 1997. A sodium bicarbonate dosing methodology for pH management in freshwater-recirculating aquaculture systems. Prog. Fish-Cult. 59, 198–205. Loyless, J.C., Malone, R.F., 1998. Evaluation of air-lift capabilities for water delivery, aeration, and desgasification for application to recirculating aquaculture systems. Aquac. Eng. 18, 117–133. Marubini, F., Davies, P.S., 1996. Nitrate increases zooxanthellae population density and reduces skeletogenesis in corals. Mar. Biol. 127, 319–328. Reynaud, S., Ferrier-Pages, C., Biosson, F., Allenmand, D., Fairbanks, R.G., 2004. Effect of light and temperature on calcification and strontium uptake in the scleractinian coral Acropora verweyi. Mar. Ecol. Prog. Ser. 279, 105–112. Sastry, B.N., DeLosReyes Jr., A.A., Rusch, K.A., Malone, R.F., 1999. Nitrification performance of a bubble-washed bead filter for combined solids removal and biological filtration in a recirculating aquaculture system. Aquac. Eng. 19, 105–117. Shashar, N., Kinane, S., Jokiel, P.L., Patterson, M.R., 1996. Hydromechanical boundary layers over a coral reef. J. Exp. Mar. Biol. Ecol. 199, 17–28. Westerman, P.W., Losordo, T.M., Wildhaber, M.L., 1996. Evaluation of various biofilters in an intensive recirculating fish production facility. Trans. Am. Soc. Agric. Eng. 39, 723–727.