Fish Handling
This section covers Fish Handling: the post-harvest changes in fish, the effect of temperature and physical abuse, and the handling steps from capture or harvest to landing and transport. The exam tests whether you can link each handling decision to spoilage, quality grade and safety.
Core rules
- Fish muscle has little glycogen; rigor mortis starts within roughly 1-7 hours depending on species, temperature and stress. Rough handling during rigor causes gaping and bruising.
- Spoilage bacteria sit mainly on skin, gills and gut. Bleeding, gutting and washing remove substrate; rapid chilling slows the rest.
- Temperature is the master variable. Use ice or chilled seawater at 0 to -1 degree C. In tropical conditions a fish-to-ice ratio near 1:1 is common, provided meltwater drains away.
- Make ice from potable water. Keep fish off the deck, out of the sun, and in insulated boxes. Do not mix bruised fish with sound fish.
Worked example
Chill 100 kg mackerel from 28 degrees C to 0 degrees C. Specific heat is about 3.6 kJ/kg per degree C, so heat to remove is 100 x 3.6 x 28 = 10,080 kJ. Ice absorbs about 334 kJ per kg when melting, so theoretical ice is 10,080 / 334 = about 30 kg. Real handling uses about 100 kg ice because of melting, box heat gain and poor contact. Reasoning: 30 kg is a lower bound, not a working recipe.
Traps
- Saying ice stops spoilage; it only slows bacterial growth and enzyme action.
- Ignoring histamine formation in scombroid fish such as mackerel and tuna.
- Stacking fish deep so meltwater warms the load.
- Using contaminated ice or freshwater that adds microbes.
- Treating gutting as a substitute for chilling.