Sorry but a few years ago I didn't work in fish research. Nowadays my area of interest is education and sustainable development.

Dear Manuel, I'm not sure how your reply is relevant to my question.

I was once told that gutted weight (i.e., body weight minus the guts) is a rough measure of total fat content in fish.

Hi Peter,

If this was true, the total fat content of an aquacultured salmon would be 90% as the gutted weight is 90% of slaughter weight. In reality, the total fat content of cultured salmon is somewhere around 15%.

Hi Bart and thanks for pointing out this interesting paper by Wilder et al. They make some good points, but get a bit wobbly when they recommend that measures of body condition index should largely be abandoned in ecological or behavioural studies (because it often poorly correlated with fat content). This, as they go on to point out that calculating condition factor has the great advantage over direct measurements of fat content that it is non-invasive.

This is the same argument/reason for why I'm interested in the fat meter (which Wilder et al seem to have missed - no reference to it in their Table 2), it's a non-invasive method, so you can e.g. follow changes in fat content in individual fish over time. Although the instrument is relatively costly, using it to measure fat content is both fast and "free", while direct measurements of fat content are both costly and time-consuming.

I haven't used it yet, but according to this paper by Goñi & Arrizabalaga (2010), measurements taken with the Distell Fish Fatmeter seem to correlate well with lipid content estimated by the Bligh and Dyer method, at least in tunas.

Article Seasonal and interannual variability of fat content of juven...

Dear Margarida,

Thanks for the reference. I'm sure that non-invasive methods such as the fat meter must be especially important in tuna research, when the individual animals may be so valuable that researchers cannot slaughter the fish just to obtain fat content measurements.

Hi Björn,

The key element when using a non-invasive tool as the fatmeter to measure body fat is the standardized measurement of well-defined body zones that need to be strictly the same for all fish if we want to be able to compare them. If this requirement is respected the fatmeter is a very valuable tool, especially if you have an important number of fish to sample.

According to my experience, measures of body condition such as Beckman's condition factor or girth/length ratio do not appear to be relevant indicators of fat content, at least for tunas.

Dear Nicolas,

Good to hear about your experience. As I'd like to use this instrument on wild salmon, who may not be so fat, especially after spawning, one of my concerns is actually the lower detection limit. How lean can the fish be? Any experience on this?

Hi Björn,

Among the 2945 albacore tunas I sampled, the lowest fat content measured was 0.58%.

Hi Björn,

I used the Distell Fish Fatmeter to evaluate small pelagic fish lipid content (mainly anchovy, sardine and sprat). It works quite well, we compared Fatmeter estimations with lipid extraction by Folch method and it correlated well.

I confirm the fact that "the standardized measurement of well-defined body zones that need to be strictly the same for all fish if we want to be able to compare them" as Nicolas said.

In the different studies, the lowest fat content that I measured was 1.8%.

Pablo

Article Measurement and analysis of small pelagic fish condition: A ...

Hej igen Björn Thrandur - first trial with fat meter now started - results seem rather good so far although we have not been able to compare with biochemical exctration analysis yet. One thing though: the use of hake as a proxy algorithm for whitefish did not work out very good. "Out of range" for most fishes we tested - probably to lean compared to salmonids - I'll keep you updated with the progress.. Take care, Alfred

how did you end up here Bjorn? did you [purchase one? How is it working?

Same thoughts from NZ around using them in a Chinook salmon project