Age determination of Buccinum isaotakii (Gastropoda: Buccinidae) from the growth striae on operculum and growth under laboratory conditions

Abstract

Buccinum isaotakii is one of the economically important whelk fishery resources in Funka Bay, Hokkaido, Japan. Although B. isaotakii has been commercially harvested for the past four decades, only very few studies were reported. In the present study, the age of the whelk, B. isaotakii, was determined based on the growth striae on the operculum. The annual formation of the stria within the operculum was confirmed by calculating the marginal growth rate. There was a significant difference ( P<0.001) between low and high monthly marginal growth of the operculum showing that a stria was possibly formed in a year. The relationship between shell length and body weight and the growth of different size classes of whelks under laboratory conditions were also examined. Both female ( W=0.000415 L 2.5292) and male ( W=0.000247 L 2.6512) whelks showed growth in shell length superior to body weight increase, showing a negative allometric growth. The parameters for von Bertalanffy growth function; length-at-age were L t =150.52{1−e −0.117( t−2.18) } for female and L t =129.99{1−e −0.132( t−2.25) } for male. For weight-at-age parameters; W t =101.03{1−e −0.117( t−2.18) } 2.5292 for female and W t =71.12{1−e −0.132( t−2.25) } 2.6512 for male. Whelks in size classes 50, 60, 70s ( P<0.001) and 80s ( P<0.01) increased significantly in shell length. All size classes except size class 100s had significant increase ( P<0.01 for 90s and P<0.001 for 50, 60, 70 and 80s) in body weight over the 12-month experimental period. The present study confirmed the use of opercular striae as age indicator in B. isaotakii and showed that the relationship between length and weight is allometric (negative) in both sexes. Smaller (immature) whelks achieved higher growth rates than bigger (mature) whelks in the tank.