Meeting Abstract
For hobbyists, fish coloration is an issue of particular importance, and can affect the value of individuals in the pet trade. Piranhas of the genus Serrasalmus are popular aquarium species among experienced hobbyists, and they exhibit a variety of coloration patterns from silver-white to gold to the very desirable purple-black. This purple coloration can vary within and among individuals, and may deepen with age. To date, it is unclear whether the source of the color is in the skin itself, or in the scales. Here, we investigate the site of purple color in 11 individual Serrasalmus rhombeus that vary in the intensity of the purple color. Deceased and frozen individuals were obtained from the commercial pet trade. To examine the source of the purple color, we measured the reflectance of each fish using an Ocean Optics USB2000 spectrometer connected to a PX-2 pulsed xenon light. We measured at four separate, standardized “patches” on the left lateral surface of each fish, first with both skin and scales intact, and then with scales carefully removed. Three of these locations were chosen because of their strong purple coloration and a fourth, ventral patch was chosen because it appeared to lack purple coloration. Scales were tested individually from only one of the four purple patches in each individual. We assessed reflectance at 5-nm intervals over the wavelength range of 300–700 nm using a 400-μm reflection probe (Ocean Optics R400-7). We found that almost all individuals exhibited reflectance that was indicative of a “true” purple color in all three treatments, scales and skin, skin only, and scales only, as well as a significant UV component. This is, to our knowledge, the first experimental investigation of color in pirhanas, as well as the first description of the presence of UV coloration in this group.
