When you're buying fish, you probably look at its color, smell it, and perhaps feel it for texture. If Martine Morzel has her way, you might also perform a mass spectrometry profile.
Morzel, of the French National Institute for Agronomic Research, was interested in what effects preslaughter activity have on the quality of resulting fillets. In typical farming practice, trout kept in a large pond or raceway are sorted, collected in a small area, and then killed, either by individually stunning and bleeding them, or in a group, by electrical shock or removal from water. As they become crowded during collection, the fish become agitated and try to escape. Several previous studies have documented the effects of this preslaughter muscle activity and stress on food quality in farm-raised or experimental tank-raised trout, salmon, and eels. Those studies concentrated on pH, metabolites, or select proteins, but Morzel wanted to cast a wider net.
So she and her colleagues compared muscle proteomic profiles of farm-raised rainbow trout (Oncorhynchus mykiss) that engaged in strenuous muscle activity for 15 minutes before death, with trout that did not (J Agric Food Chem, 54:2997-3001, March 28, 2006). Using a combination of two-dimensional gel electrophoresis and mass spectrometry, the group identified 29 differently regulated proteins, 27 of which were downregulated in the exercised group relative to the control group 45 minutes after death, including energy production pathway members such as triosephosphate isomerase and structural proteins such as Cap-Z and desmin.
These changes, especially the lower abundance of desmin, a key cytoskeletal protein, could be molecular indicators of a lower-quality fillet, according to the authors. In other words, "such a preslaughter treatment can have an effect on postmortem muscle integrity," they write.
So what do fishmongers at Philadelphia's famous Reading Terminal Market, think of the findings? Naython Brown, who works behind the counter at the Golden Fish Market, hadn't read the study, but then, his company sells wild fish. "We think farm-raised is less healthier than wild." Wan Woo, owner of Wan's Seafood, also hadn't had a chance to read the study. But he says he's never had a problem with the quality of his farm-raised rainbow trout. Standing in front of his stall packed with salmon, shrimp, and of course, trout, Woo says the trout is "very firm."
Certainly, "mistreating [fish] prior to slaughter" can lead to poor quality, says Randy Macmillan, president of the National Aquaculture Association and vice president of research at Clear Springs Food in Buhl, Idaho, the world's largest producer of rainbow trout for human consumption. But, "I would argue that there's no evidence at all that rainbow trout harvested from farms in the US are of poor quality," he says. "In fact, in today's market, demand [for farm-raised trout] is so high that it can't be met."
Many variables can affect the quality of fish, Macmillan says, including the sex of the animals, the food they ate, the time of year, degree of sexual maturation, and the temperature of the water. US fish farmers also don't anesthetize the fish before killing them, as Morzel did, to reduce preslaughter muscle activity.
Most importantly, Macmillan notes, the authors do not actually demonstrate a correlation between exercise and what he calls the "organoleptic qualities of the fish" - that is, its taste, texture, and smell. Morzel says her collaborators and coauthors have demonstrated that "the texture is softer in the same conditions as the one which we used here," and says a paper to that effect is in preparation.
Either way, don't expect to see proteomics profiles on your fish packaging anytime soon. As long as fishmongers and their customers are happy with the product, practices aren't likely to change, at Reading Terminal Market or anywhere else. Still, says Samuel D'Angelo, co-owner of Ippolito's Seafood in south Philadelphia, "Knowledge is always a great thing. If there's something that can be done better, obviously I'm open to it."