2016 Volume 3 Issue 2 Pages 29-39
Understanding the growth, fecundity and survival, as well as population density, is the basic knowledge for conserving threatened species. By counting the annuli on the scales, we estimated the age of the threatened piscivorous cyprinid fish, Amur three-lips (Opsariichthys uncirostris uncirostris), in Lake Biwa located in central Japan. A total of 169 individuals were caught, including 111 males, 56 females, and two for which the sex was undetermined. To estimate the growth of the three-lips, we used data from 56 males and 28 females caught during a single reproductive season (late May to early August 2013). The estimated maximum standard lengths and growth coefficients were 274.20 mm and 0.25 for males and 269.23 mm and 0.22 for females, respectively. The growth curves of the standard lengths were expressed using von Bertalanffy's growth equation by using the estimated variables. We compared our growth equations to those in a previous study conducted in the 1970's. The results indicated that the relative growth rates of the three-lips decreased in 1- and 2-year-old fishes. In addition, we found that fishes that were 3-years and older were shorter in average length than those in the previous study. We suggest that the current decline in growth rate of the three-lips is associated with the decline of fish prey resources because of changes in the habitat driven by human activities as well as the invasion of competitive exotic fishes, such as the largemouth bass (Micropterus salmoides), over the recent past decades.
