Abstract
The analysis of marine plankton have been worked out by BRANDT (1898), BRANDT and RABEN (1919-22), MEYER (1914), MOBERG (1926) and WIMPENY (1929) for its protein, fat, ash, carbohydrate or chitin contents. The seasonal variation of fat and protein contents of Calanus in Clyde Sea-Area was recently studied by ORR (1934), MARSHALL, NICHOLLS and ORR (1934). On the other hand, KNAUTHE (1901), NAKAI (1921) and BIRGE & JUDAY (1922) have given analytical data of fresh water plankton and benthos. The inorganic constituents and protein digestiblity of Crustacea, Mollusca, Worms, and other organisms as fish foods have never been studied. The present paper deals with the chemical composition of them with special reference to their inorganic constituents, namely, calcium, magnesium, phosphorus, iron, copper, sulphur, and iodine contents, chitin, and the protein digestibility. Thirteen kinds of organisms were analysed by using ordinary methods for total nitrogen, protein nitrogen, crude fat and crude ash content. R. PINCUSSEN'S micro-method (1928) was employed for determining the amounts of inorganic constituents. Chitin was measured by using the method of BUXTON (1932). The kinds and analytical data are given in Tab. 1.
Comparative study of protein digestibility was made by using pepsin and eel protease which was extracted from stomachal membrane of Anguilla japonica (optimum temp. 37°C, opt. pH 3.2).
For the digestibility the soluble nitrogen liberated during digestion at 37°C was taken as a measure. The pH value of digestive mixtures were held at 2.0 for pepsin and at 3.0 for the eel ferment using citrate buffer solution.
The protein digestibility (D) was calculated by the following formula: D=S1-S0/N×100, where S0 and S1 are amounts of soluble nitrogen at outset and 24 hours afterwards respectively, and N denotes the total nitrogen of the samples. The results of the experiment are given in Table 2 and 3, and shown in Fig. 1. It will he seen from Fig. 1 that similar digestibility is obtained either by pepsin or by eel ferment. It is also to be seen in the same figure that chitin content of the material is reversely correlated with the protein digestibility.
