Two fish, two larvae

01 · Analyses

What was analysed

Kajaani University of Applied Sciences (KAMK) procured three rounds of black soldier fly (BSF) rearing trials on Kainuu fish side streams. Larvae from the successful fish recipes of the final round were frozen whole at harvest and analysed in an ISO/IEC 17025-accredited laboratory: basic composition, amino acids, fatty acids, minerals and heavy metals. Differences between recipes within one raw material were small, so the results are read per raw-material group.

02 · Composition

Lean versus fatty

Crude protein, % of dry matter

Lake fish side stream

48.2

Trout filleting side stream

40.7

Trout gut mass (estimate)

44.1
Crude fat, % of dry matter

Lake fish side stream

24.7

Trout filleting side stream

41.0

Trout gut mass (estimate)

31.6
Ash, % of dry matter

Lake fish side stream

8.5

Trout filleting side stream

5.8

Trout gut mass (estimate)

8.9
Moisture, % of fresh weight

Lake fish side stream

65.4

Trout filleting side stream

60.6

Trout gut mass (estimate)

59.0
EPA + DHA, g/100 g fresh weight

Lake fish side stream

0.41

Trout filleting side stream

0.60

Trout gut mass (estimate)

0.24

Lake-fish larvae were lean and protein-dense. Their 48 % crude protein in dry matter is above the typical range reported for whole BSF larvae (about 28–44 %), and their 25 % fat is below it (about 29–52 %). Filleting-side-stream larvae were fatty: 41 % protein and 41 % fat. The fat of the filleting side stream moved into the larvae. The lake-fish stream is lean and bony, which shows as more ash, calcium and phosphorus in its larvae. Gut-mass larvae fall between.

Larval moisture, 59–65 %, was below the usual figure for live larvae (about 70 %), so a fresh kilo carries more dry matter.

A note on protein: total amino acids were 74–78 % of crude protein. Part of the nitrogen is chitin and other non-protein nitrogen, so the standard N × 6.25 factor overstates true protein by about a quarter. The factor proposed for insects, N × 4.76, matched the measured amino acid sum within 3 %.

03 · Amino acids

Same amino acid profile

The share of each essential amino acid in total amino acids varied by less than half a percentage point between the groups, which is within measurement uncertainty. The fish stream changed the amount of protein per kilo, not its quality. Lake-fish larvae held 25 g of lysine and 7.3 g of methionine per kilo of dry matter; filleting-side-stream larvae 19 g and 5.1 g. Lysine, at 6–7 % of amino acids, is good. Methionine and cystine together stay under 3 %: as usual for BSF larvae, the limiting group in feed formulation.

04 · Omega-3

Omega-3: real, but moderate

Lake-fish and filleting-side-stream larvae both contained measurable EPA and DHA: 0.41 g per 100 g fresh weight on lake fish and 0.60 g on the filleting side stream, or 12 and 15 g per kilo of dry matter. Literature reports very little EPA and DHA in BSF larvae reared on ordinary plant-based feed, so this is enrichment carried over from the fish. It is moderate. These larvae do not replace fish oil.

The filleting-side-stream larvae carried less lauric acid than typical BSF larvae (14 % of fatty acids against about 35–41 %), and 65 % of their fatty acids were unsaturated. For a fresh or frozen product, that makes oxidation control part of the design.

05 · Conditions

Two conditions for use

Raw fish side streams are not a permitted substrate for insects reared for feed or pet food in Finland today; fishmeal is. And the mercury in lake-fish larvae exceeded the general limit for feed materials, while the filleting-side-stream larvae were well below every heavy-metal limit (the mercury findings).

06 · What this means

What this means

The raw material shapes the product before the larvae do. Lake fish points to a lean protein ingredient, if its mercury is managed; the filleting side stream to an energy-dense ingredient with omega-3, if oxidation is managed.

All results are in the summary report. If you have a side stream you want evaluated, get in touch.

About the project: Kajaani University of Applied Sciences (KAMK) procured black soldier fly larvae rearing trials on Kainuu fish side streams as part of the KALARVO project (Processing fish side streams into value products). Manna Insect carried out the trials as the contractor, responsible for the trial design, measurements and analysis. Co-funded by the European Union.