In this study, we examined the life history characteristics of the parrotfish Calotomus japonicus, using individuals collected between May 2003 and May 2008 off the Nagasaki Peninsula in northwest Kyushu, Japan. Age determinations were performed using scales. Marginal increment analysis revealed that growth rings were formed annually around July. Growth in both sexes was fitted to the von Bertalanffy growth function (L ? = 513, k = 0.28, t 0 = 0.03, where L ? is the theoretical asymptotic total length in mm, k is the growth rate coefficient and t 0 is the theoretical time at zero length). Observed maximum age for both sexes was 8 years. We also characterized the reproductive biology of this species based on a gonadosomatic index and histological examinations of the gonads. The spawning season extends from July to October, with peak spawning activity occurring during July and August. Fish reach sexual maturity by the second year of life. Females are assumed to be multiple spawners, since we observed specimens with postovulatory follicles in ovaries containing either yolk globule oocytes or migratory nucleus oocytes. All males had secondary testes, which were characterized by the presence of an ovarian lumen structure and sperm sinuses in the gonadal wall. This indicates that all males, irrespective of whether they were initial or terminal phase males, had undergone a sexual transition. Sex change appears to occur during the spawning season, and thereafter sex-changed males are able to fertilize female eggs throughout the remainder of the current spawning season.

No abstract

Determining the population parameters of herbivorous fishes facilitates our understanding of their overall effects on ecosystems. However, this has not been successful with species such as Kyphosus bigibbus that are difficult to age using otoliths. In this study, we estimated the age, growth and age at sexual maturity of K. bigibbus off the west coast of Kyushu, Japan, using fish scales and otoliths. Scales were found unreliable because they caused underestimation of the age of fish older than 5 years, whereas otoliths were reliable when used with our improved otolith-sectioning methodology. The maximum age and fork length were 46 years and 574mm for females and 32 years and 506mm for males. According to the von Bertalanffy growth curves, females became slightly larger than males, and both sexes showed nearly asymptotic fork lengths after 10 years. The age at 50% sexual maturity for females and males was 3.2 and 1.9 years respectively, which is extremely early considering their maximum age. The year-class composition of K. bigibbus suggests that its recruitment may have increased rapidly since 1999, following noticeable losses of kelp forests in this region. Our findings will contribute to the understanding of algal forest ecosystems and advancement of fish ageing studies.

Nomozaki, where a relatively high-density seaweed patch remained, and were tracked for more than 4 months using a biotelemetry system. During the survey, signals from the S. fuscescens were recorded with high frequency in the daytime and with low frequency at night. These was a similar trend of signals from K. bigibbus, but nove was recorded at night. The total signals per day decreased when the water temperature fell to 20°C for S. fuscescens and to 16 17°C for K. bigibbus. The movement patterns of S. fuscescens and K. bigibbus may change with water temperature, however, they still stayed around the seaweed patch oŠ Nomozaki during the winter and never migrated.There is a possibility of causing serious damage to seaweed during autumn and winter, because the activity ofˆsh extended over a long period of time as a consequence of the recent rise of water temperature.

The reproductive characteristics of Kyphosus bigibbus were examined using individuals collected between June 2004 and February 2009 off Nagasaki Peninsula in northwest Kyushu, Japan. The spawning season and size at sexual maturity of this species were characterized based on a gonad index and histological examination of the gonads. The spawning season extends from June to October. This species is assumed to be an indeterminate, multiple-batch spawner. Females reached sexual maturity at larger size than males (fork length at 50% sexual maturity: males 284 mm, females 360 mm).