The Relationship of Food Intake to the Stomach Contents in the Mackerel, Scomber japonicus

Abstract

The food intake and its relation to the stomach contents at the time of feeding in the mackerel, Scomber japonicus were studied by using the fishes of about 31 ?? 26 gr body weight which had been well trained to eat pieces of anchovy meat to the full in net cages set up in the sea.
Starvation in the strict sence of the word was thought to start in this species of fish after 3.5 days of fasting, when the total stomach weight reached the minimum (Fig. 2). The food intake in weight in starved fish was about 23% of the body weight at the highest and 16% in average when they were satiated with anchovy meat at about 20°C. The stomach contents decreased rapidly with time, reaching about 20% of the initial weight after 5 hours and 1.8% after 10 hours (Fig. 3). The digesive process was completed in 21 to 24 hours (Fig. 4). pH of stomach contents was about 6.7 before feeding and was reduced rapidly after feeding, reaching 4.1 after 7.5 hours.
Fishes took food actively even though part of the foods which they had previously taken remained in their stomachs. The amount of the intake was inversely proportional to the amount of the residues (Table 1, and Fig. 5). This suggests that digestion curve may be determined from feeding curve in the mackerel.