The document discusses fish cooking theory and provides guidelines for cooking different types of fish based on their fat content. It explains that lean fish with low fat, such as cod and haddock, are best poached, deep fried or baked in a sauce, while fattier fish like salmon and tuna can be baked, grilled or pan fried. The fat content of fish determines the best cooking method. It also classifies fish according to habitat and fat storage location.