Despite the larger maximum size of the ark shells from Nanao Bay compared with those from Sendai Bay, the maximum age of the ark shells from Nanao Bay was far younger than that from Sendai Bay.
In this study, the estimated maximum age of ark shells from Nanao Bay was 6 y old.
Flowever, the estimated maximum age of ark shells from Sendai Bay in this study was 20 y, which is far older than the age estimated by substituting the largest size of collected specimens into the von Bertalanffy growth model obtained using shell outer growth ring data (i.
The shell growth patterns of ark shells did not differ significantly between the northern and southern areas of Sendai Bay.
The shell growth rates of ark shells were fastest for the Nanao Bay population, followed by the Sendai Bay population and then cultured individuals from Mutsu Bay (Table 1, Fig.
In the present study, histological observations of the gonads of subcrenated ark shells in Ariake Bay revealed that gametogenetic development of the male and female commenced in April, when the water temperature had reached 17[degrees]C.
The spawning period of subcrenated ark shells in our study was shorter than that in Kasaoka Bay (Ting et al.
Interestingly, high glycogen content was maintained during the spawning period, and large numbers of developing oocytes were often present in the subcrenated ark shells after spawning.
ABSTRACT The reproductive biology and glycogen content of a subcrenated ark shell Scapharca kagoshimensis (Tokunaga, 1906) in Ariake Bay were investigated from April 2004 to May 2005 in relation to environmental factors such as water temperature, salinity, and plankton settled volume.
KEY WORDS: subcrenated ark shell, Scapharca kagoshimensis, gametogenesis, reproductive cycle, glycogen content
Although gonad mass was consistently low in ark shells up to a shell length of about 50 mm, the gonad index increased at 18-20 mm in shell length (up to 32%), indicating the onset of gonad production.
The observations of seasonal changes in gonad indices for the four different size groups of ark shells further showed that 10-30 mm individuals had negligible reproductive output, and that 30-50 mm individuals had substantially less output than larger individuals.
ABSTRACT Over the period from June 2002 to June 2003, we examined the relationship of seasonal changes in the mass of the gonad and somatic tissues to environmental factors for four size groups of the zebra ark shell Arca zebra at Chacopata, in northeastern Venezuela.
For each ark shell, we first removed the byssus and secondly removed epibionts and detritus from the shells.
Although the thermograph we placed on the ark shell bed only functioned from July to December 2002, the record was sufficient to show that the temperature record from the NOAA satellite provided a good approximation of temperatures at our study site (Fig.