Fish Products and By-products
This section covers Fish Products and By-products: value-added products such as surimi, fish sausage, fish sauce and pickles, and by-products such as fish meal, fish oil, fish silage, chitin, chitosan, isinglass and glue. The exam tests product flow, yield and the quality risk specific to each product.
Core rules
- Fish meal is made by cooking, pressing, drying and grinding. Yield is typically about 20-25 percent from whole fish, with oil recovered from the press liquor.
- Fish oil is prone to oxidation; control temperature, exclude air and add antioxidant where permitted. Measure peroxide value and free fatty acid.
- Chitin is extracted from shrimp and crab shell by demineralisation, deproteinisation and decolourisation; chitosan is deacetylated chitin.
- Fish silage is produced by acid or enzyme digestion. It is a liquid feed ingredient, not a human food.
- Fish sauce relies on salt and enzymatic fermentation; histamine and salt control are critical.
Worked example
Process 1,000 kg trash fish. Meal yield 22 percent gives 220 kg meal; oil yield 6 percent gives 60 kg oil. At Rs 40 per kg meal and Rs 90 per kg oil, revenue is Rs 8,800 + Rs 5,400 = Rs 14,200. Raw fish at Rs 8 per kg costs Rs 8,000, leaving Rs 6,200 before processing costs. Reasoning: calculate each product separately, then compare total revenue with raw material cost.
Traps
- Using spoiled scombroid fish for meal and risking high histamine.
- Ignoring oil oxidation during storage.
- Calling chitosan the same as chitin.
- Forgetting shell washing before chitin extraction.
- Pricing a by-product without accounting for drying energy.