The IPHC has been investigating the incidence of chalky halibut in landings from the commercial fisheries since 1996.  Overall, chalkiness ranges from over 10 percent in landings from Washington and Oregon, to around 5 to 10% in landings from Canada, to less than 5% in landings from Alaska.  The causes of chalkiness are not well understood, although it is likely that a combination of factors are involved, including exhaustion in the fish (which increases lactic acid in the flesh, and thus overall acidity of the flesh), water or air temperature when captured, and the handling routine on the fishing vessel.  Work done with the IPHC in the late 1960's showed a very close correlation between highly acid flesh and the development of chalkiness. The problem of chalkiness is increased by the fact that the condition may take from 3 to 7 days after death to develop in the flesh.  These pictures came from fish caught during an IPHC experiment in the fall of 1999.  The experiment was designed to test the effects of stunning and bleeding on the development of chalkiness.  When fish were caught, they were individually tagged and either stunned, bled, stunned and bled, or given no treatment.  These fish were purposely held for at least 3 days, and in some cases up to 10 days (from capture til processing) in order to allow the chalky condition to fully develop.  We intend to have a preliminary analysis of the experiment by early 2000.

Most of these pictures show a very striking difference between chalky and non-chalky fish.  Keep in mind that these fillets have had days postmortem for the condition to fully develop.  In many cases, especially when fish are sold and processed just a day or two after capture, chalkiness may be much less evident.

In the picture on the left, the left fillet is not chalky.  The flesh is transparent.  The right fillet in the picture is chalky.  The flesh is an opaque white.  This is an extreme case of chalkiness, and has had a number of days to develop postmortem.  Remaining blood, particularly around bones, is very evident in a chalky fillet.

Chalkiness can be determined during initial processing by making a shallow cut just below the dorsal fin.  Lifting the skin with the knife allows a visual inspection of the flesh.  In a test conducted with the IPHC, cuts like these were used to determine the chalkiness in 1312 halibut.  114 fish were determined to be chalky.  Of the 114 fish initially determined as chalky, filleting revealed that 1 fish was not chalky, 95 fish were fully chalky, and 18 fish were partially chalky.  A subsample of the fish initially determined to be non-chalky was later filleted.  Out of 82 fish determined non-chalky by the knife cut, 4 fish were partially chalky and 1 fish was fully chalky.

Chalkiness can be very evident as soon as the fillet cut is begun.  These fillets are chalky.

This fillet is only partially chalky.  Chalkiness has developed particularly along the top of the fillet back and to the tail end.  The lower portion of the fillet is still translucent.

[Left picture} The carcass on at left is from a chalky fish.  the carcass at right is from a non-chalky fish.  The fillet is chalky.  It is possible to see the translucence in the flesh of the non-chalky fillet. [Right picture] The difference in color and translucence of the non-chalky (left) and chalky (right) carcasses is very evident.
 

This is a tote being filled with chalky fillets.  With proper handling, these fillets can be sucessfully marketed, although at greater cost to the processor.  Often, chalky halibut can be portioned and breaded to make a product which is appealing to the consumer, and every bit as tasty and nutritious as products made from non-chalky halibut.
 

Chalky fillets
 

The roast on the left is chalky.