The Kashrus of Skinless Salmon

June 13, 2013

This column has previously addressed the concern of purchasing fish without its skin intact. We discussed that once the skin is removed, one has no way of knowing what a particular fish is, unless it was skinned in the presence of a mashgiach. As such, a skinless fish is considered “kirvei dagim” (unidentifiable fish), and is forbidden m’drabannan (see Y”D 83:5). We also pointed out that some major kashrus agencies allow for an exception to this rule. We mentioned that these agencies view the red color of salmonid fish (salmon, steelhead, arctic charr) as a siman muvhak of kashrus1 even when the skin is removed. These agencies maintain that all red-fleshed fish are kosher, and that so long as one has no reason to believe the fish was altered in any way, one can accept it as kosher even without skin.

Presently, a great deal of the commercial salmon is not captured from the wild, but rather it is raised on a salmon farm. This process, known as aquaculture, seeks to raise salmon to be as similar to wild salmon as possible. In nature the salmon’s red flesh color comes from a carotenoid that wild salmon absorbs (amongst its other dietary staples) from ingesting shrimp, lobster, or krill. Farmed salmon however, lack this element from their diet, and without supplementation would be pale instead of an appetizing red. Though this pale salmon is perfectly healthy, marketing experts found that consumers would generally prefer to buy salmon whose looks share the ruddy hue of wild salmon.

Therefore despite a significant increase in expense , synthetic2 versions of the carotenoids astaxanthin and canaxanthin are added to the salmon’s diet to help bring color to its flesh.

Knowing that synthetic carotenoids are able to create a red color in salmon has lead some to question the propriety of accepting red colored flesh as a siman of kashrus in fish. If synthetic carotenoids can be used to “dye” salmon flesh couldn’t they be used to color the flesh of non-kosher fish as well? In its efforts to continue to research the matter, the OU embarked on a fact-finding mission, to consult with field experts in order to determine whether or not this concern was justified.

Most of the researchers we contacted in the U.S., Canada and Norway (the three primary areas of farmed salmon research) noted that in nature many fish live in the same habitat as the salmon and share similar diets. Despite this fact, we see that the carotenoids they ingest do not pigment their flesh. It may on occasion color their skin3 but their flesh will remain white. This indicates that these fish are naturally incapable of depositing astaxanthin into their flesh.

Dr. Bjørn Bjerkeng4 reported that that after having been personally involved in multiple experiments of astaxanthin feeding trials with white-fleshed fish species (types of fish that do not naturally metabolize carotenoids the same way as salmonids do), he found that even ingesting large quantities of carotenoids could not color the fish flesh. Though the other fish may deposit small amounts of pigment in their flesh this would not be enough to mimic a salmon.

The majority5 of the researchers contacted concluded that there is no reason to be concerned that someone could feed astaxanthin to non- salmonid fish and color their flesh. Dr. Remi Baker6 explained that salmon muscle is able to bind astaxanthin unlike the muscle tissue of other types of fish. Although other fish maybe able to incorporate small amounts of astaxanthin in their flesh through a passive process the salmon is unique in its ability to actively attach the pigment to its flesh.

Dr. Hannah Rajasingh7 provided the lone dissenting opinion. She wrote, “If any fish is fed very high levels of carotenoids it would end up having a pinkish-red tinge to its flesh.” She compared this to the phenomenon known to take place in human skin when large amounts of carotenoids are ingested. She did note that the experiments on halibut, catfish etc. have shown that non-salmonid fish are not able to pigment their flesh when normal levels of astaxanthin are added to their diet. Her basis for this assertion was an article by S. Applebaum8 describing an experiment in which catfish were fed high levels of astaxanthin which added some color to its flesh. It is important to note that she agreed that even when fish were subjected to high levels of astaxanthin as was done in Applebaum’s experiment the fish would not become anywhere near red enough to mimic the flesh of a salmon or trout. Furthermore, other experts questioned the validity of the article in the first place noting that there was no indication it was submitted for peer review. Additionally Dr. Bjerkeng pointed out that the article did not tell anything about carotenoid levels, but rather only about relative concentrations. He added, “the absorbance of the carotenoids treatments are rather unimpressive compared to the control and my guess is that it is not [sic] looking anything like properly coloured salmon.”

Dr. Baker and Dr. Lall9 agreed. They noted that the catfish in the experiment started off very pale and even though it absorbed four times as much pigment by the end of the experiment this would still leave it very pale. Even with the extremely high level of pigmentation in its feed the catfish did not obtain the level of pigmentation that a salmon would have. Moreover, both of them pointed out that although the catfish may be able to absorb the pigment it would not be able to bind the astaxanthin it its flesh and retain the color as explained previously. Thus the white fleshed fish would revert back to its pale color soon after they stopped feeding it the carotenoid. Dr. Rajasingh concluded that feeding the non-kosher fish high levels of astaxanthin to market them as salmon would be at least economically unfeasible10 .

Several researchers11 confirmed that the scientific mechanisms that enable only the salmonids to deposit astaxanthin into their flesh are not well known. Dr. Bjerkeng wrote that based on recent reports and his own experimentation, he believes that the reason for the differences among different species of fish is due to “uptake at the muscle cell level”, and “receptor expression”. He added that metabolic transformation rate also plays a role. Though the mystery has not yet been solved, he is optimistic that future research will reveal the reason why apparently only salmonids were created with the ability to deposit carotenoids into their muscle tissue.
In short, the consensus of researchers expert in the area of carotenoid absorption conclude that there is no concern of carotenoids (or any other coloring agent) being fed to a non-kosher fish to color its flesh and substitute it for salmon.
A second potential concern is that someone would inject dye into the flesh of a non kosher fish to make its flesh red.

In fact there are companies in Norway which dye strips of Saithe and sell it as an imitation smoked salmon. Couldn’t someone also do this to a whole raw fish?
In order to properly evaluate this concern, we must break down and analyze every aspect individually. The first point we must evaluate is if there exists a traif fish that is similar enough to salmon that when dyed it could be substituted for salmon12 . In fact many of the available sources of non kosher fish vary greatly in size from salmon. Catfish for instance is much smaller than salmon and would be too small to even slice into lox13 . Eels, sharks, monkfish and sturgeon are also not of similar size to even potentially be passed as a salmon.

Next we must compare the differences found in the flesh itself. Differences in texture, grain, moisture levels, oil content and fat line are often found which would prevent other fish from being substituted for salmon. This is the case with sturgeon as the texture of its flesh is not comparable to that of the salmon. Texture of the fish’s flesh is a very important determinant of how the fish will accept and spread the dye as well.
The flesh of monkfish and of a catfish for example, is relatively soft to begin with making it harder to inject dye into such a fish. Some thought the flesh might “turn to mush” if injected and also noted that there would be difficulties with the dispersion of the dye because of the meat type. The density of the flesh also plays a significant role in the acceptance of the dye. Some thought shark would not take the dye because its flesh is so much denser than that of the salmon.
Some have suggested that softer fish could simply have color applied by soaking the fish in brine or by having the color sprayed on. It is important to note that fish that are not injected could only hold color on the outside, but the color would not be absorbed throughout the fish. For this reason needles are needed to get to the dye into the middle of the fish. This can sometimes leave another telltale sign that the fish has been dyed. This would be holes or slits placed every half inch or so.
After the injection is administered the fish is often soaked in a cover brine of dying solution to even out the injected color, which does not spread out evenly in the fish’s flesh. This brine is a blend of dye, salt and preservatives. The dyed fish will retain the salt creating another obvious indication the fish has been dyed. If the fish were not soaked in brine or saltless brine was used, it would be easy to tell that the fish had been injected. For one reason without salt the flesh would become rather mushy, (salt reduces the moisture level, keeping the flesh in tact better). In addition, there would be an obvious asymmetry in the color (the salt serves as a carrier which helps the dye migrate to all parts of the fish). For this reason dyed fish are usually smoked.

Technological advances have not yet found a way to stop the color from coming out of the fillet during cooking. Since people would surely notice the fish was dyed after they started cooking it dyers would be forced label the fish as such, otherwise they would surely be caught committing economic fraud. This reason alone would prevent even the most unscrupulous fish seller from adulteration.

Additionally, one must consider whether there is a motivation for one to commit economic fraud by dying non-salmon in order to sell it as salmon. Sturgeon is more expensive than salmon so there would be no motivation to commit economic fraud and sell it at a lower price. Anyone who tried this would not be in business too long. Even the dying of a cheaper fish should not be a major concern. There aren’t many traif fish that are significantly cheaper than pale salmon. In addition, someone caught adulterating fish in this way (as opposed to simply “switching” a more expensive species for a cheaper one) would undoubtedly suffer significant consequences if caught.

FDA and Department of Agriculture inspectors inspect plants regularly. For troublesome companies and individuals who are suspected of fraud they visit more often. Packaging that does not say color added may not contain dyed products and, as mentioned, the FDA does enforce this law. In addition they would need to falsify records and this would result in serious legal consequences for those who are caught. Also, the industry itself practices self-policing as companies perform self reviews. This makes it much harder to get away with economic fraud and the harsh penalty should deter those who would otherwise take the risk.

Clearly the risks of economic fraud would outweigh the potential reward of a small financial gain. Moreover, one must note that there would be other technological investments necessary in order to carry out this type of scam. To make an imitation salmon fillet that mimics the real thing would be very difficult when dealing with a generation accustomed to the eating of authentic salmon.

In conclusion, those organizations accepting salmonids as kosher without skin have sound reasons to maintain this policy in the face of the various concerns addressed above. Some may disagree with this conclusion. However, it is important to realize that throughout Shulchan Aruch, a Rav is always expected to judge based on realistic concerns, not on the theoretical. It is the job of responsible Rabbonim, and kashrus certifying agencies, to investigate potential concerns and evaluate the situation at hand. In this case, it is clear that if you’ve caught a fish “red-fleshed”, it is still the same salmon you thought it was.

1 This is not an extension of the Beis Yosef’s mesorah regarding red fish roe (see Shulchan Aruch 83:8 and Shach ad loc. #27). See DafHaKashrus Vol XI:8 article by Rabbi C. Goldberg March 2003.

2 Experts estimate the increased cost of adding carotenoids to salmon feed at being between 10 and 25% of the entire feed cost, adding significantly to the retail price of the fish.

3 Rabbi Goldberg noted that cantaxanthin has been marketed previously as an artificial tanning pill, as humans deposit free carotenoids in their skin, the similar to the way that salmon deposit them in their flesh.

4 Of AKVAFORSK in Norway which is a leading institution for research, in the field of aquaculture. He was recommended as “the world’s leading capacity in this field”, an “astaxanthin expert” and has written a review article entitled “Carotenoid pigmentation of salmonid – recent progress.”

5 Experts familiar with the way carotenoids work (and able to cite proofs to this effect) confirmed that they believed that salmonids were alone in their ability to absorb carotendois in this way.

6 The resident technical expert for carotenoids who is located in the BASF Germany HQ and is a member of the BASF Global Tech Services team.

7 From the Center of Advanced Genetics at the Norwegian University of Life Sciences (UMB). She coauthored an article about carotenoid dynamics in Atlantic salmon with Dr. Våge who disagrees with her.
fn8. of the Ben-Gurion University of the Negev

9 Group Leader, Aquatic Animal Health & Nutrition/ Principal Research Officer National Research Council Institute for Marine Biosciences.

10 Several of the other experts also pointed this out. One noted this would double the cost of catfish feed.

11 Dr. Bjerkeng, Dr. Hatlen (of AKVAFORSK) and Dr. Baker.

12 The information that follows was gathered through conversations with Mr. Alan Levitz of Banner Smoked Fish, Ms. Karen Evich of Q Sea Specialty Services, Mr. Donald Rader of Three Star Smoked Fish Co. Inc and Dr. Meyer a senior OU Mashgiach.

13 The significance of lox will be discussed later on.


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