World Aquaculture 9 Mithraculus forceps larvae (photographed by Gil Penha-Lopes) Productivity improvement of red clinging crab Mithraculus forceps through modeling Joana Figueiredo1 A worldwide increase in the popularity of reef aquariums within the past decade has resulted in increased demand for marine ornamental species for the aquarium hobby trade. The aquarium trade is a billion dollar business that may sustain continued growth for years. The majority of organisms, 90 percent, are still harvested from the wild, particularly from highly threatened coral reefs in Southeast Asian countries where their collection represents a profitable income for natives. Destructive collection techniques include poisoning with cyanide and physical destruction of the reefs. Additionally, many animals die in transit before getting to retailers or home aquariums. Fortunately, legislation to protect ornamental species and certifications to control the business has been increasing (Cato and Brown 2003). To reduce the pressure on the natural environment and satisfy the growing demand of hobbyists, inexpensive rearing techniques of highly prized and priced species needs to be developed. Captively raised animals are more resilient than wild animals as they are accustomed to aquarium conditions and often readily consume prepared food, such as pellets or flake food. For these reasons, hobbyists may be willing to pay extra for environmentally habituated animals. Presently, the percentage of commercially cultured ornamentals is still limited to a few fish species, mainly clownfish of the genus Amphiprion, some corals and a few marine decapods. Organisms most desired by hobbyists for their home aquariums can be divided into four groups: the most beautiful and colorful such as clownfish, angelfish and surgeon fish; the strange and weird looking such as seahorses and eels; ones which blend in with the aquarium and challenge us to find them such as frogfish and stonefish and finally, the cleaners that assure your aquarium remains healthy, for instance. Organisms exhibiting cleaning behavior include pest controllers like the sea slug Berghia verrucicornis, peppermint shrimp Lysmata wurdemanni and Monaco shrimp Lysmata seticaudata, all of which control the pest glass-anemone Aiptasia pallida. The emerald crab Mithraculus sculptus and red clinging crab Mithraculus forceps control the pest bubble algae Valonia and Ventricaria (Figueiredo et al. in press). Other cleaners include macroalgae grazers, such as the scarlet reef hermit crab Paguristes cadenati and the scavengers and detritivores that include the bumble bee snail Engina sp. and Nassarius snail. Aquaculture research tends to focus on the biological aspects of culture and often overlooks the production perspective when a culture protocol is developed. Some of the major goals required to aid the aquaculture industry are the optimization of protocols, particularly large scale culture, and production prediction. Modeling offers the advantage of using data from studies previously published to make predictions. As opposed to statistical analyses that will only reveal the relationships among the data, a model can offer a deeper understanding and simplified picture of reality and yield a better management plan. The biological aspects of culture are important to producers; however, this information needs to be adjusted for production. As an example, some of the questions for which a producer would like answers in larval culture include the following. What are the most productive abiotic and biotic conditions for larval rearing? How many juveniles will one obtain at the end of larval culture to initiate grow-out? Models, as opposed to statistical analysis, allow not only the comparison of survival to juvenile of the larvae produced, but also predict metamorphosis synchronism and day metamorphosis begins. Rather than using final survival to evaluate how good a certain condition, for instance stocking density, productivity should be used. For example, for a 10 L tank, considering we have an unlimited supply of larvae, using a stocking density
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