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.

Context. Eleutheronema tetradactylum is exploited throughout its distribution in the Indo-West Pacific region. However, there is a lack of data on its life cycle in near-equatorial regions and the northern hemisphere. Aim. To investigate the age, growth, sex change and reproduction of Eleutheronema tetradactylum in southern Thailand. Methods. Analysis of length, otolith and gonad data of 449 fish. Key results. Contrary to findings from regions at higher latitudes, otoliths did not show seasonal increment formation. Instead, with the exception of large individuals, daily increments were distinguishable. Within the age range of 69-341 days, growth was linear, with results indicating a total length of 430 mm (69% of maximum length) at 1 year. The youngest mature male was 137 days old. Moreover, the length at which half the individuals changed from male to female was 376 mm, corresponding to 282 days. The gonadosomatic index indicated no specific spawning season, and the hatch-date calculations indicated year-round hatching. Conclusions. Eleutheronema tetradactylum inhabiting near-equatorial regions is characterised by rapid population turnover compared with populations of higher latitudes. Implications. Our findings indicated life-history variability, including seasonality loss in near-equatorial habitats, of an important coastal fish. This information is important for species conservation.

Tiger pufferfish Takifugu rubripes (order Tetraodontiformes, family Tetraodontidae) is a highly exploited species and stocks continue to decline, although hatchery-reared juveniles have been released since 1965 for stock enhancement. To determine why the stock has not recovered through hatchery-release practices, this study investigated and compared the population characteristics of wild and hatchery-origin fish.The length-mass relationship showed that hatchery-origin fish were skinnier, with males weighing less than 90% of the mass of wild males of the same length. The hepatosomatic index tended to be lower in hatchery-origin fish. Age was estimated using the otolith-based method, and the estimates were more accurate and precise than those obtained by the conventional vertebra-based method. At the age of 2.9 years, an age at which specimens were the most abundant in catches, hatcheryorigin males weighed only 67% of wild males. The maximum observed age was 12 years for wild fish and 5 years for hatchery-origin fish. The instantaneous total mortality rates of hatchery-origin fish were more than twice as high as those of wild fish. In summary, the hatchery-origin fish had poor health status, poor growth and high mortality, and their fitness in natural environments was therefore hypothesized to be low throughout life.

No abstract