Whole salmon, 2.4 fish and a full freezer
You run the fish section of a 90-cover bistro. Whole line-caught salmon is $22.00/kg and your supplier sends fish of about 6.5 kg. Portioned skin-on fillets are $42.00/kg, vacuum packed in 1 kg packs with a four-day shelf life. Your filleting yield is about 62% in two fillets, 8% belly and trim, and 30% head, frame, skin and bones. Belly is currently binned; frames go into the stock pot, and the kitchen buys in fish bones at $6.00/kg to cover the shortfall. Filleting takes a commis about 25 minutes at $22.00/hour fully loaded. The bistro sells 60 salmon portions a week at 160 g. The walk-in has 1.2 m of shelf for raw fish and the freezer is full. The chef-owner asks whether whole fish will cut the food cost - and whether it is 'the sustainable choice'.
1. Do the numbers for one fish and then for a week at 60 × 160 g portions. Is whole fish cheaper?
Read the worked answer
One 6.5 kg fish: 6.5 × $22.00 = $143.00.
- Fillets: 62% × 6.5 = 4.03 kg usable → $143.00 ÷ 4.03 = $35.48/kg before labour.
- Labour: 25 min at $22.00/hour = $9.17 → $9.17 ÷ 4.03 = $2.27/kg → $37.75/kg all in.
- Belly/trim: 0.52 kg. Head, frame, skin, bones: 1.95 kg.
Against $42.00/kg portions, that is a saving of about $4.25 per usable kg - but that is only the first half of the calculation.
Weekly demand: 60 × 0.160 kg = 9.6 kg of fillet. At 4.03 kg per fish you need 2.38 fish. You cannot buy 0.38 of a fish.
- Three fish: 12.09 kg usable, cost $429.00 + labour $27.51 = $456.51. If you sell 9.6 kg and bin the 2.49 kg surplus, the true cost of what you actually sell is $456.51 ÷ 9.6 = $47.55/kg - worse than buying portions.
- Three fish with the surplus sold (a special, a cured belly, a staff plate priced into the menu): the cost stays at $37.75/kg, and you gain 3 × 1.95 = 5.85 kg of frames and heads, displacing roughly $35 of bought bones.
- Two fish: only 8.06 kg, so you top up with a 1 kg pack of portions and lose the simplicity argument.
The answer is not the filleting yield - it is the 2.49 kg surplus. Whole fish is cheaper only at near-total utilisation or at higher volume.
2. What operational and sustainability conditions must hold for whole fish to be the better choice, and what would you actually do with the belly, frame and skin?
Read the worked answer
Operational conditions:
- Skill and consistency - fillets must be even enough to give a 160 g portion; a wobbly first fillet costs more than the commis's 25 minutes.
- Storage - 1.2 m of shelf and a full freezer means three fish must be broken down and either sold inside two to three days or frozen, and freezing changes texture and your 'fresh' claim.
- Menu flexibility - someone has to want the surplus. If the menu cannot absorb it, the maths fails.
- Volume - at 9.6 kg a week you are at the awkward level; at 25 kg a week the surplus is a rounding error.
Sustainability conditions - this is a separate question from cost:
- Stock status and certification (MSC/ASC or the local equivalent), and the gear: line-caught generally carries lower bycatch and seabed impact than trawled.
- Provenance and transport distance, and whether the fish is in season.
- Utilisation, which is where your kitchen currently fails: binning the belly is a 'prevent' failure in the waste hierarchy and it is money.
What to do with the parts: belly and trim (0.52 kg per fish) → cure, grill as a staff/bar snack, or render for a dressing; head and frame (with the skin and bones) → stock, then bones out; skin → crisped as a garnish or for crackling. The waste hierarchy is prevent → re-purpose → recycle → dispose, and every kilo you re-purpose also deletes a purchased input (the $6/kg bones).
3. The owner says: 'So we're sustainable now, right?' How do you answer?
Read the worked answer
No - we are better on waste and possibly on cost, and that is not the same thing.
Three reasons to say it plainly:
- Cost is not a sustainability measure. A cheap fish from a collapsing stock is a bad choice at any price; the price signal does not carry stock status, gear type or bycatch.
- Whole-fish buying only helps if the whole fish is used. If the 2.49 kg weekly surplus goes in the bin, you have swapped a tidy cost line for a larger waste stream - the opposite of the intended result.
- A claim on a menu has to be defensible. 'Sustainable salmon' on the specials board is a marketing statement and a customer could reasonably ask you to evidence it. If you cannot name the fishery and its certification, do not print the word.
What I would actually say: 'We're better on utilisation and we've cut a purchase, and we still need to confirm the certification and whether the surplus gets sold or binned. Let's measure it for a month - kilos bought, kilos sold, kilos binned, and the certification - before we put anything on the menu.'
That answer keeps the improvement and keeps the honesty. 'We're sustainable now' is the sentence that stops you checking.