On the Biology ofCalanus finmarchicus. Part IV. Seasonal Changes in the Weight and Chemical Composition in Loch Fyne

Abstract

1. The dry weight of 100 male, female and Stage V Calanus in Loch Fyne fluctuated throughout the year. 100 Stage V Calanus in May weighed only about ⅓ of what they did in December. Male and female Calanus also fluctuated considerably in weight.2. Stage V Calanus is usually largest and heaviest when it is most abundant. With male and female Calanus size and weight are related.3. Stage V Calanus, in spite of being smaller than female Calanus, was from the beginning of June till the end of August considerably heavier (over 100%). When Stage V Calanus was at its lightest and smallest, it weighed less than female Calanus at the same time.4. The weight of Stage V Calanus fell during the spring and did not increase again till after the end of the first breeding period.5. The fat and protein content of Calanus depends chiefly on dry weight. The values obtained for fat content were considerably higher than those hitherto recorded for zooplankton and those of protein lower.6. The ash content is about 3·6% and the chitin content about 3% of the dry weight.7. Stage V Calanus accounted for by far the most important part of the total weight of the catch throughout the year.8. The total food value of the Calanus in Loch Fyne probably varies very considerably from year to year.