1. Historical Review.- The Role of Fish in Research on Genetics and Evolution.- 2. Sex-Determination and Melanoma Formation.- The Sex-Determining Mechanism of the Platyfish, Xiphophorus maculatus.- Preliminary Report on Sex Differentiation in Germ Cells of Normal and Transplanted Gonads in the Fish, Oryzias latipes.- Regulation of Gene Expression in the Gordon-Kosswig Melanoma System.- I. The Distribution of the Controlling Genes in the Genome of the Xiphophorin Fish, Platypoecilus maculatus and Platypoecilus variatus.- II. The Arrangement of Chromatophore Determining Loci and Regulating Elements in the Sex Chromosomes of Xiphophorin Fish, Platypoecilus maculatus and Platypoecilus variatus.- 3. Mutagenesis.- Radiation Damage in Fish.- Dominant Lethal Mutation Rates in the Fish, Oryzias latipes, Irradiated at Various Stages of Gametogenesis.- Chromosome Manipulation in Fish.- Teleosts as a Tool in Mutation Research.- 4. Chromosomes and Cytology.- Chromosomes of Two Fish-Species of the Genus Diretmus (Osteichthyes, Beryciformes: Diretmidae).- The Chromosomes of Some African Anuran Species.- Incorporation of H3-Thymidine into the DNA of Melanotic and Amelanotic Melanoma Expiants after Whole-Body X-Irradiation of Melanoma-Bearing Platyfish-Swordtail Hybrids.- Fate of Bacterial DNA Injected into Embryos of Poeciliid Fish.- Regulation of the Pigment Cell Arrangements in Species and Interspecies Hybrids of Xiphophorus (Pisces, Poeciliidae) by Cellular Interactions on the Fish Body.- Experimentally Induced Sexual Maturity in Artificially Reared Male Eels (Anguilla anguilla).- 5. Ethology.- Change of Aggressive Readiness in Post-Irradiation Generations of the Convict Cichlid Fish, Cichlasoma nigrofasciatum.- Attraction and Sexual Cycle of Poeciliids.- 6. Evolution.- Genetic Problems in the Regressive Evolution of Cavernicolous Fish.- Phylogenetic Age and Degree of Reduction of Cave Animals.- Origin and Synthesis of a Unisexual Fish.- Fish and Nature's Extensive Experiments with Gene Duplication.- 7. Biochemistry.- Biochemical Polymorphism and Microevolution Processes in Fish.- Developmental and Biochemical Genetics of Lactate Dehydrogenase Isozymes in Fishes.- Biochemical Evolution in the Genus Xiphophorus (Poeciliidae, Teleostei).- Tissue-Specific Preferential Expression of the Xiphophorus xiphidium Allele for 6-Phosphogluconate Dehydrogenase in Interspecific Hybrids of Platyfish (Poeciliidae, Teleostei).- Investigations on the Serum Polymorphism of Trout and Carp.- Inheritance of the S-Form of NADP-Dependent Isocitrate Dehydrogenase Polymorphism in Rainbow Trout.- Biochemical Variants in Pacific Salmon and Rainbow Trout: Their Inheritance and Application in Population Studies.