エゾアワビの生態学的研究-I

Abstract

1) A study on the food habit of the abalone, Haliotis discus hannai Ino, an industrially important gastropod in northern Japan, has been made by feeding it with 7 species of brownalgae, 2 species of green-algae, 3 species of red-algae, and diatom. 2) It has been clarified that brownalgae such as Undaria pinnatifida, Laminaria religiosa, Colpomenia bullosa are the most suitable food for H. discus hannai in respect to its growth and the efficiency of its food conversion. Green-algae, Ulva pertusa and Enteromorpha linza come next in the food value. Red-algae such as Pachymenia sp., Rhodoglossum pulcherum, Carpopeltis affnis etc. and brown-algae, Sargassum fulvellum are inferior in value as food for H. discus hannai. Melobesiae has also been found effective in the shell formation of the adult shellfish. 3) Diatom such as Melosira borealis or Navicula sp. has been found to be a suitable food even to adult abalones and they grow sufficiently well with this food alone. 4) When 2 species of algae are simultaneously given to abalones, they prefer Ulva pertusa to C. afinis, and Undaria pinnatifida to Ulva pertusa, showing some likes and dislikes. Generally speaking, when a mixed food is given to abalones, their growth are inferior to the growth of abalone, fed with algae which are superior as food. 5) It has been assumed that the optimum temperature for the growth of H. discus hannai is within the range of 15-20°C. 6) The efficiency of food conversion at the water temperature of 10.5°C has been found to be 5-8% (12-21% in calorie equivalence) for abalones of 20-30g in weight fed with Undaria pinnatifida and 9-11% (24-29 cal. %) for ones of 60-90g in weight, and the case fed with Pachymenia sp. shows 8-13% (7-11 cal.%) and 22-31% (20-28 cal.%) respectively, and in either case large sized abalones have shown higher rates, but the rates secured the stability at least between 50-100g in body weight. 7) For maintaining the body weight of abalones, necessary daily rates of feeding with U. pinnatifida are 1.75% (0.42% in calorie equivalence) and 0.65 (0.15 cal.%) respectively, for the ones of 20-30g and the ones of 60-90g in weight, and in the case fed with Pachymenia sp. 0.82%1 (0.53 cal.%) and 0.08% (0.05 cal.%) respectively. These rates are smaller for the larger sized abalones. 8) The relation between the species of food and the maturation of gonad of abalones is in exact conformity with the relation between the species of food and the growth rate of abalones, and the food suitable for the growth of the shell also brings a good result to the maturation of gonad. 9) No significant difference in the chemical composition of the meat of abalones due to the species of food has been found, but it has been found that the content of glycogen is greater in those fed with U. pinnatifida or L. religiosa than those fed with other foods. 10) When H. discus hannai are fed with brown-algae, green-algae and diatom, they form a shell of bluish-green color. On the other hand, when they took red-algae, brown colored shells resulted without exception. When they are fed with brown-algae and red-algae alternately, the shells turn into bluish-green color and brown color alternately.