18 DECEMBER 2015 • WORLD AQUACULTURE • WWW.WAS.ORG So far, 46 species of seahorses have been described and the majority of species share overlapping distribution ranges. In areas where distribution ranges overlap (contact zones), the question of unknown hybridization is of concern. In recent years, two aquaculture laboratories have confirmed hybridization between seahorse species and another confirmed a case of hybridization occurring in the wild. Because of the varying degree of phenotypes commonly found among hybrids, multivariate analysis has been useful in studying the range of morphology among hybrids. Morphometric studies indicate that hybrids may have greater phenotypic variation than either parent species. This morphological data can then be coupled with genetic analysis of parent species and hybrid offspring to further validate the correct identification of hybrid individuals (Ho et al. 2015). Seahorses follow unconventional length measurements such as snout length, trunk length, tail length and ring counts (Fig. 3, left). Additionally their bony plates create defined ring counts that, when combined with traditional morphometric measurements using discriminant function analysis (DFA), can help correctly identify the parent species, in this case the lined seahorse, the longsnout seahorse H. reidi and their hybrids (Fig. 3, right). The recent identification of the potential for seahorses to hybridize may show additional benefits of culturing seahorses, as hybrids have shown in many other taxa. Benefits could include better growth rates, better response to traditional feeds like brine shrimp and selection for desirable traits such as larger sizes or specific coloration. However, there are many captive seahorses that are currently maintained and exchanged among facilities as part of captive breeding programs for conservation. In such programs, hybridization has to be curbed and the threat of unknowingly introducing hybrid animals into breeding programs for conservation have been established to supply the aquarium trade market, the real solution for seahorse conservation lies in mass production to meet the demand of TCM in China. Large numbers of seahorses are consumed for medicinal purposes in China, as more studies find support for their pharmacological benefits (Chen et al. 2015). In recent years, over a dozen large-scale commercial seahorse aquaculture facilities have emerged in China. Upon returning to China in recent years, two of the postdoctoral fellows and research associates in our lab, Dr. Qiang Lin and Dr. Dong Zhang, have spearheaded the efforts to revitalize seahorse aquaculture industry there by providing technology support. Largely due to their efforts, dozens of large commercial-scale production companies have sprung up in the last two to three years, producing up to a million seahorses a year and numbers are increasing at a fast rate. With a better grasp of general aquaculture practices and commercial-scale viability, recent research is focused on finetuning culture methods by looking closer at the sensory systems and how these may affect culture. Seahorses are born as predators and are reliant on sight for prey capture. This means that light intensity can have substantial effects on survival and growth by mediating hunting and feeding strategies and by influencing early eye development (Delabbio 2015). The revolution in light-emitting diode (LED) lighting technology now allows for a cost-effective way to adjust light intensity and light quality. Furthermore, LED lighting allows the use of a more variable array of light intensities and wavelengths than standard incandescent and fluorescent lights. Various conditions that replicate light intensities in marine ecosystems were established using energy-efficient LEDs to study the effects of light intensity on juvenile lined seahorses. Subjecting separate groups of newly-released seahorses to different light intensities, and measuring predation success gives us better insight about the light intensities that may benefit seahorses during this most crucial life stage (Fig. 2). How seahorses perceive their environment is vital for prey capture. There are two types of photoreceptor cells. Rods function best in dim-light environments and cones function best in brightlight environments. As development of the eye progresses, different light intensities may become beneficial or disadvantageous due to variable rod and cone densities. Recently we found that the density of rods and cones in seahorses differ through developmental stages as well as in different areas of the eye (Lin and King 2015). The development of a greater understanding of the retina in seahorses will aid in further identification of optimal environmental lighting for seahorse aquaculture. FIGURE 3. Seahorse morphometrics to discriminate among H. erectus, H. reidi and their hybrid (left). Relative positions of seahorse specimens in plots of discriminant function 1 versus discriminant function 2. The discriminant function analysis resulted in accounting for all the observed variance (69 percent in the first and 31 percent in the second function). Classification indicated that functions could accurately assign seahorses to species group 88 percent of cases. Individual group accuracies were 97 percent for H. erectus, 81 percent for H. reidi and 88 percent for hybrids. Photo by Adeljean Ho and Deanna Derosia.
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