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Juvenile Dover sole, Solea solea, were weaned from a live food, Artemia salina nauplii, on to a casein-based particulate diet flavoured with flesh of the mussel, Mytilus edulis. These fish would not accept an unflavoured casein-based diet but readily ate the diet flavoured with either mussel flesh or a mixture of pure chemicals whose composition was based on an analysis of the low-molecular weight fraction of mussel flesh. The rate of growth and survival over a seventy-seven day period was essentially the same on either of the flavoured diets. The active constituent in the mixture of pure chemicals was identified as glycine betaine for fish of wet weight exceeding 5 0 g while glycine betaine with certain L-amino-acids was required for fish of about 2.5 g wet weight. These results are discussed in relation to the known feeding behaviour and food preferences of the wild Dover sole.

Gadusol, C8H12O6, has been isolated from roes of the cod (Gadus morhua L.), i.e., ovaries that contain ripe eggs just before spawning. The concentration is about 4 g/kg dry wt. It has been identified as 1,4,5-trihydroxy-5-hydroxymethyl-2-methoxycyclo-hex-1-en-3-one and this structure was confirmed by synthesis of the anhydro tetra-acetate derivative from methyl 3,5-diacetoxy-4-methoxybenzoate. Concentrations of gadusol in the roes of other marine teleost fish examined are of the same order as in cod roes. Gadusol has some properties similar to ascorbic acid and both compounds, after oxidation, react with 2,4-dinitrophenylhydrazine in the commonly-used assay procedure for ascorbic acid. Specific assays showed that the concentrations of gadusol in the roes of marine fish are severalfold greater than those of ascorbic acid. Gadusol is structurally related to the mycosporines previously reported from a number of different organisms.

A system for the quantitative study of the learning capacity of rainbow trout and its application to the study of food preferences and of behaviour. Groups of trout were selftrained in about 10 days to actuate a trigger and feed themselves. This capacity was retained for 3 months without the stimulus of continuous reinforcement. Presented with a choice, conditioned populations showed a high degree of discriminatory ability towards a trigger that supplies food and one that does not. The choice system was used to examine preferences for the taste of pelleted foods. A trained population, under continuous illumination developed a feeding rhythm that occurred about every 8 h.

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