Comparison between surface-reading and cross-section methods using sagittal otolith for age determination of the marbled sole Pseudopleuronectes yokohamae

Abstract

Title:Comparison between surface-reading and cross-section methods using sagittal otolith for age determination of the marbled sole Pseudopleuronectes yokohamae Authors:Jeong-Hoon LEE ABSTRACTTo find an appropriate method for age determination in the marbled solePseudopleuronectes yokohamae in Tokyo Bay, Japan, sagittal otoliths of 1343 individuals were observed by surface-reading and cross-section methods and the results were compared. Opaque zones occurred once a year and were regarded as annuli in both methods. The surface-reading method sometimes provided a lower count of the number of annuli than the cross-section method, and the frequency of this discrepancy was highest in older fish (males above 5 years, females above 4 years). The oldest female fish was estimated to be age 10 years by the cross-section method but 8 years by the surface-reading method. The cross-section method could provide a more accurate estimate of age and is therefore likely to be indispensable to estimations of longevity. In contrast, the surface-reading method is superior in terms of cost and time efficiency but is likely to underestimate the ages of older fish. However, growth equations based on age estimated by the surface-reading method were sufficiently accurate if males ≥ 5 years and females ≥ 4 years were combined as specific, single age groups of 5+ and 4+, respectively. KEY WORDSAge determination, Cross-section method, Growth, Otolith, Pseudopleuronectes yokohamae, Surface-reading method, Tokyo Bay 3 INTRODUCTIONThe marbled sole Pseudopleuronectes yokohamae distributed in Japan from southernHokkaido to Oita Prefecture in Kyushu, as well as in the Yellow Sea, the Bohai Sea, and the northern part of the East China Sea [1]. In Tokyo Bay, Japan, P. yokohamae is the dominant species in the megabenthic assemblage and is a highly valued fish species exploited by commercial fishers in the bay [2,3]. However, despite the importance of P.yokohamae as a commercial resource, the abundance of this species has markedly decreased since the late 1980s. According to statistics from the Shiba Branch of Yokohama City Fisheries Cooperative Association, the annual catch of P. yokohamae in Tokyo Bay exceeded approximately 500 t in the mid 1980s, but by the 2000s it had decreased substantially to around 50 t. Therefore, there is a need for elucidation of the cause of the decline of P. yokohamae for the recovery of the stock in the bay.To understand mechanisms of the population dynamics of P. yokohamae in Tokyo Bay, we have to clarify the critical life-history stage (or stages) that determine the year-class strength, and identify factors that affect mortality during the critical life-history stage, as well as consideration of changes in life history traits (e.g., reproduction), which may contribute to the population decline. In studying these matters, age and growth is one of important life history traits [4,5].For the estimation of age and growth, establishment of an accurate aging procedure is indispensable. Age and growth of P. yokohamae have p...

Age determination of Atlantic halibut (Hippoglossus hippoglossus L.) along the coast of Norway: status and improvements

“…Sectioning of otoliths was useful when the whole otoliths were damaged above or below the core, as an age can still be interpreted from the section in those cases. Previous ageing studies performed for a number of species have found that otolith surface readings underestimate age (Blood, 2003;Albert et al, 2009;Lee et al, 2009). Although we did not find any evidence of this in our study, most of our samples were from relatively young fish (,9 years).…”

Life history of a simultaneously hermaphroditic fish, Diplectrum formosum

“…The difference could be attributed to Bortone (1971) estimating ages of D. formosum using whole otoliths while this study sectioned the otoliths before reading. Sectioning otoliths provides more accurate estimates of age in fishes, which have high initial growth early in life, such as the D. formosum , due to the allometric change in otolith growth, which causes the outer increments to be obscured when read whole because of their proximity to each other (Beamish, 1979; Peltonen et al , 2002; Lee et al , 2009). Latitudinal and regional variation in age and growth could also be a factor (Conover & Present, 1990) between the western Atlantic Ocean, where fish for this study were collected and the Gulf of Mexico, where Bortone (1971) collected samples.…”

Changes in growth of marbled sole Pseudopleuronectes yokohamae between high and low stock-size periods in Tokyo Bay, Japan

“…Sagittal otoliths from the blind side of the fish were used for age determination and subsequent growth analysis. These otoliths are suitable for reading annuli because the innermost opaque region is located in the center of the otolith [7]. They were immersed in 50% glycerol 6 solution and observed under reflected light against a dark background using a stereomicroscope at 16× magnification (SZX-ILLB100; Olympus Optical Co., Ltd, Tokyo, Japan).…”

“…They were immersed in 50% glycerol 6 solution and observed under reflected light against a dark background using a stereomicroscope at 16× magnification (SZX-ILLB100; Olympus Optical Co., Ltd, Tokyo, Japan). The number of annuli (opaque zones) on the otoliths was regarded as the age, because previous studies [3,7] have shown that the number of annuli indicate age in marbled sole. The opaque zones are formed only once a year between January and July [7].…”

“…The number of annuli (opaque zones) on the otoliths was regarded as the age, because previous studies [3,7] have shown that the number of annuli indicate age in marbled sole. The opaque zones are formed only once a year between January and July [7]. We used a digital camera attached to the microscope to capture images of sagittal otoliths, and these images were used to measure the otolith radius (R) from the center to the postrostrum.…”