Contents: 1. Introduction. 2. Mendel’s laws of inheritance. 3. Inheritance of qualitative traits in fish. 4. Cells and chromosomes. 5. Genes. 6. Gene interactions. 7. Genetics of quantitative inheritance. 8. Sex determination. 9. Sex linked genes. 10. Hybridization in fishes. 11. Mitochondrial inheritance. 12. Mutation. 13. Linkage and crossing over. 14. Chromosome manipulation. 15. Cryopreservation. 16. Population genetics. 17. Inbreeding and crossbreeding. 18. Domestication in fishes. 19. Sex-Reversal in fishes. 20. Selection methods in fishes. 21. Genetic improvement of fish and shell fish for disease resistance. 22. DNA markers in fisheries application. 23. Aquatic genetic resources and its conservation. 24. Fish seed certification and quarantine