Deliciously pink fish

January 2019

British scientists seem to be heavily into improving farmed fish these days. They might have preferred to feed us GM fish (the patents would be worth a bob or two), but Frankenfish aren't going to feature on consumers' wish-list any time soon so they're settling for GM fish food additives instead [1].

The 'problem' the latest GM venture is trying to solve is that fish in the wild eat all sorts of different things which can end up in, and colour, their flesh all manner of pinks and oranges. Farmed fish have a very boring and unnatural diet, and end up fish-coloured, that is white or pale grey.

To the consumer, however, pink is healthy: no one's told them that grey is just as good.

In order to make farmed fish saleable, farmers have long added pink dye derived from petrochemicals to the feed to give their fish, as one journalist described it, "their delicious colour". The trouble is petrochemicals and any synthetic food additives derived from them are increasingly taboo.

Enter GM to generate a somehow "non-artificial" pink-coloured fish food additive in a plant.

Since tomato fruit have a good capacity to make red colours, the plan is to feed farmed fish with tomatoes. Not just your average salad variety, but one with two bacterial genes in it which together drive ten biochemical reactions in the fruit to generate the desired pink stuff.

In tests, the GM-tomato-fed fish grew well, and in biochemical and physiological analyses were deemed 'substantially equivalent'. Unexpectedly, the fish fed on extracted, concentrated GM dye attained only half the degree of delicious colouring as did fish fed dried, powdered whole GM tomato.

COMMENT There's clearly a lot more to whole food chemistry and its digestion than we can know from our simplified, reductionist understanding of individual components.

To give the journalist the last word:
"The enterprise says something about the cultural and scientific moment we're in - turning to genetic modification to replace a petroleum-based product that is used to compensate for the removal of a natural process".


The super-red GM tomatoes have 'Cauliflower Mosaic Virus' (CaMV) promoters attached to the artificial genes [2,3]. Whether this novel DNA, or side-effects from the planned or unplanned bio-active substances in the GM tomatoes are problematic for the GM tomato, for the GM-fed fish, or for us (or for all three), we'll likely only find out the hard way.

According to the Oxford English Dictionary, "Delicious" means 'Highly delightful, especially to taste, smell or the sense of humour". Tomato-hued fish won't taste or smell any more delightful than the plain grey ones, but you might find a sense of humour is needed to deal with the side-effects.


[1] GM VEGGIE OIL FOR FISH - November 2018

  • Marilise Nogueira, et al., October 2017, Engineering of tomato for the sustainable production of ketocarotenoids and its evaluation in aquaculture feed, PNAS 114
  • Kat Eschener, Genetically Modified Tomatoes Give Fish a Futuristic Hue, Hakai Magazine, 3.07.18
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