Seasonality in digestive-gland size and metabolism in relation to reproduction in Haliotis kamtschatkana

A novel method of isolating digestive grand cells in abalone was used to pr ovide information on the metabolic activity of this gland in Haliotis kamts chatkana. Activity, expressed as percent change in Vo(2) of isolated cells before and after the addition of glucose and amino acid substrates, was stu died in relation to sex and to seasonal changes in gonad and digestive glan d indices. At 3- to 4-mo intervals between May 1995 and July 1996, five col lections of 10 adult abalone (equal sexes) were made from the West Coast of Vancouver Island, British Columbia. Each animal's live mass (without shell ) was recorded, and its gonad was aspirated from the digestive gland into a known volume land mass) of seawater. The digestive gland was sliced free o f its attachment, weighed, and related to shelf-less body mass as percent d igestive gland index (DGI). The gonad live mass was determined from the mas s of aspirated mix of gonad and seawater, and related to shell-less body ma ss to give a percent gonad index (GI). Digestive gland cells were prepared and maintained in a special buffer, and their Vo(2)'s measured in microresp irometers. There was no sex effect on seasonal DGI, but significant seasona l differences in DGIs correlated perfectly with metabolic activity of diges tive-gland cells with glucose substrate. Thus, when digestive glands were l argest relative to body size, metabolic activity of their cells was greates t. GIs were significantly higher for males than females. There was a signif icant seasonal effect on GIs, with Values being high in springtime before s pawning (April to May, 10-11%) and low in winter (December, 6%), but with s tatistical overlap between these and summer values (July to August, 7-8%). Metabolic response of the digestive gland cells was highest with glucose su bstrate (75% increase over presubstrate resting levels as compared with 4% for amino acid substrate), reflecting the carbohydrate-based metabolism of abalone.