Mackerel at 34 °C: a landing-centre intake decision

Decision: reject the lot for canning; divert to fish meal (or hold it only if a buyer will accept a delayed histamine result).

Reasoning chain:

• Time–temperature history is the decisive fact. The fish spent roughly 11.5 h from capture to landing, with the first 5 h at about 34 °C with no ice. At those temperatures the optimum for bacterial growth and for decarboxylase-producing bacteria is fully met.
• Scombroid risk. Mackerel is a scombroid species. Histamine forms when free histidine is decarboxylated by bacteria such as Morganella morganii; once formed, histamine is heat-stable, so canning will not inactivate it. A canning buyer is therefore buying a product for which a later histamine result cannot be corrected by processing.
• Sensory evidence matches the history. Soft flesh, brown gills, sunken eyes and separation of flesh near the backbone are consistent with advanced autolysis and bacterial action, not with a single incidental delay.
• Test timing does not fit the commercial deadline. The ELISA result arrives 24 h later, while the truck leaves at 06:00. Sampling also cannot prove a 1,200 kg lot is uniformly below 100 ppm when the history is so unfavourable.
• Value comparison. ₹95/kg is attractive, but a rejected or recalled canned lot costs far more than the ₹18/kg meal outlet. Take the certain ₹18/kg and log the rejection.

If any fish are kept for testing, hold them separately, labelled non-conforming, and never mix them with compliant stock.

Sensible heat to remove:

Q = m × c × ΔT = 1,200 kg × 3.7 kJ/kg·K × 26 K ≈ 1,15,440 kJ

Ice required if every gram of ice absorbed its full latent heat:

m = 1,15,440 / 334 ≈ 346 kg

That 346 kg is a floor, not a working figure, because it ignores:

• meltwater draining away before it can absorb heat;
• heat entering through the basket walls and the tarpaulin;
• the heat capacity of the baskets and the container;
• continued bacterial and enzymatic heat production in the fish;
• the need to hold the fish near 0 °C for the remaining hours of the trip, not merely to touch 0 °C once.

Good tropical practice is roughly 1:1 ice to fish, i.e. about 1,200 kg for this landing, with the ice layered and the meltwater drained.

Why 300 kg failed: 300 kg is about 0.25:1, roughly one-quarter of the basic requirement and a small fraction of the working requirement. The ice melted early, the meltwater ran off, and the fish never fell below about 20 °C during the critical first hours. The failure is one of quantity and of layering, not of the ice itself.

Records to complete:

1. Intake/landing record: date, time, vessel and supplier identity, species, weight (1,200 kg), ice-to-fish ratio declared, core temperatures measured (24–27 °C), sensory observations, thermometer identification.
2. Disposition record: rejected for canning, quantity diverted to fish meal, price realised (₹18/kg), signature of QC and of the plant head.
3. Non-conformance and supplier report: reason for rejection, the HACCP clause on histamine and the time–temperature requirement, sent to the supplier the same day.

Corrective action required from the supplier: the vessel must carry and use ice from the moment of capture and land fish at or below 4 °C. In practice this means insulated boxes or a chilled-seawater hold, ice loaded before sailing, and a temperature log at landing. Add a verification step: for the next three landings, measure core temperature and record it, and suspend purchases if the standard is not met. This converts a one-off rejection into a monitored supplier specification.