Analyses of the free amino acids, quaternary amines, guanido compounds, nucleotides, nucleosides, and organic acids in extracts of tissues from 10 species of marine teleost fishes and 20 species of invertebrates are reported. With multidimensional scaling techniques, the relative concentrations of the above chemicals in fishes, molluscs, and crustaceans are shown to cluster into separate taxon-specific groups. The greatest differences are between the fishes and the two groups of invertebrates. Similarities are more evident between the molluscs and crustaceans where eight of the nine most abundant substances are identical: i.e., betaine, taurine, trimethylamine oxide, glycine, alanine, proline, homarine, and arginine. The major tissue components in the fishes and invertebrates are correlated with compounds previously shown to stimulate feeding behavior in 35 species of fish. Glycine and alanine are major tissue components and are also the two most frequently cited feeding stimulants in the 35 species. Molluscs and crustaceans each contain high concentrations of five of the most frequently cited stimulants (glycine, alanine, proline, arginine, and betaine); these substances all occur in much lower concentrations in fish. Some minor tissue components, such as tryptophan, phenylalanine, aspartic acid, valine, and uridine 5`-monophosphate, are, however, important feeding stimulants for some fish species. Stimulants for herbivores and carnivores are often different. Several major feeding stimulants are substances that serve as "compensatory solutes," stabilizing enzymes and structural proteins.

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Scanning electron microscopy was used to survey the aesthetasc tuft on the outer flagellum of the antennule (1st antenna) in order to identify sensilla potentially involved in pheromone detection by the male blue crab. These studies showed that the tuft of each antennule is divided into a mesial and lateral half by a region of cuticle from which no sensilla arise. Two setal types were revealed: the aesthetascs and previously undescribed sensilla which originate exclusively on the mesial side of the tuft and project to the lateral half between the rows of aesthetascs. Experiments were performed in which the mesial half, lateral half, or entire aesthetasc tuft was bilaterally ablated from the antennules of test males. As revealed by behavioral tests, pheromone responses in "mesial half 1 and "lateral half ablation groups were reduced 22% and 21%, respectively, relative to control (P > 0. 10); whereas a highly significant (P < 0.005) response decrement (80% relative to control) occurred in the "entire tuft" ablated group. The data suggest that pheromone reception in the male blue crab is effected via the aesthetascs. The relationship of these findings to those for other decapod crustaceans is discussed.