Since 1997, we have produced annual documents describing
out chalky halibut investigations. You can link to them in
PDF format here:
Pacific halibut is fished by setline (long strings of line with attached hooks) on the continental shelf from northern California to the Bering Sea. The fishery currently operates eight months each year, from mid-March through mid-November. Chalky halibut has been recognized for decades, although until recently the problem was limited to summer fisheries in the southern fishing areas off Washington and Oregon. Until 1995, landings in most areas have occurred during short fisheries in the early and late summer, and most product was frozen. Since 1995, fisheries occur throughout the open period, and a majority of the product is sold fresh. This, combined with an increased awareness of chalkiness by the marketplace, has created the current situation, where as much as two million pounds of the 60-million pound catch is graded as chalky and thus unmarketable, constituting a multi-million dollar loss to the industry.
IPHC research, both in the 1960s and in the last five years, have shown chalkiness to be directly associated with a buildup of lactic acid and resulting lowered pH in post-mortem flesh. The condition is specifically associated with a denaturation of muscle proteins resulting in an increased drip loss and a sometimes startling loss of translucence in the flesh. In extreme cases, the flesh gapes, and has little use as a food product. Our research has associated chalkiness with two areas of the coast during late summer and early fall, and male halibut tend to be chalkier than females. It is likely that the areas with the highest rate of chalkiness are associated with high bottom temperatures (12-14 degrees C), which are near the upper thermal limit for the species’ distribution. Most recently, we have facilitated the use of pH meters in 1-2 day post-mortem fish to determine flesh pH, which is predictive of the developing chalky condition.
The condition is reversible in live
fish. Flesh which would otherwise likely be chalky does not develop the
condition post-mortem if the fish are allowed a 1-2 day resting period
after capture, and before killing.
Description of "chalky" halibut · flesh is "soft and flabby", has a dull, flat, ‘chalky’, opaque white color, contrasted to the firm, shiny, semi-translucent white flesh of non-chalky fish. · on cooking, chalky halibut is dry and fibrous compared to non-chalky. · chalky condition varies in degree, both between fish and within a single fish.
The flesh of ‘chalky’ fish is indistinguishable from that of normal fish at time of capture, at least in terms of visual, pH, or protein extractability. The change to the chalky condition is dependent on the muscle pH. Acidity levels (pH) are directly related to levels of lactic acid in the flesh. Lactic acid is a byproduct of the conversion of glycogen into energy. Buildup of lactic acid is associated with fatigue. Rest after exertion results in a decrease in lactic acid levels. A fish which dies immediately after a high activity period will have high levels of lactic acid (low pH) and is likely to be chalky. (BUT: lactic acid is formed from glycogen postmortem: Tarr, 1968). A rest period, such as lying on the hook after capture, will lower lactic acid levels and reduce the chances of chalkiness. Well fed fish would have high energy reserves (glycogen). These fish may exercise more strongly at capture, producing higher lactic acid levels. Chalkiness is more frequent in trawl caught fish. These fish would have died after or been subject to extreme exhaustion.
Lactic acid theory · well-fed or heavy-feeding fish with high glycogen energy reserves · extreme physical activity causes large accumulation of lactic acid (fatigue byproduct) · removal of lactic acid is impeded or blocked · the higher the holding temperature, the more intense the condition and the more rapid its development. · resultant change in muscle proteins · NOTE: this is similar to a condition in rabbit, pig, beef, or whale meat. A well fed animal killed under physical struggle or stress conditions had similar meat degradation.
Experimental results · Trawl
caught fish, brought on board dead, were tagged. At landing, visual and
pH observations were recorded. Of 113 fish, 56 were ‘slightly chalky’ and
57 were ‘very chalky. Observations of pH of dorsal slab were made (Myhre,
IPHC, notes) · <3 hr set, longline fish were not stunned immediately,
8 % of 88 fish were chalky (rep by Patashnik) · Tomlinson et al
(ref 1) did an extensive experiment with trawl caught and some longline
caught fish. · Freezing fish immediately after capture and dressing,
on thawing flesh is indistinguishable for first 2 hours, then goes opaque.
This change in appearance was accompanied by a decrease in pH and in protein
extractability. · There was a tendency for the muscle pH or longline
fish to be higher than trawl fish at time of landing on vessel. ·
Tomlinson (ref 3) allowed trawl-caught but still alive halibut to recover
in a holding tank for 10 to 13 hours. Flesh was stores 11 days on ice.
After storage, flesh from recovered fish had higher pH, and lower percentage
were chalky (46 vs 77% and 0 vs 33%).
References
Bell, F. H. 1950. Notes regarding "milky", "mushy", and "chalky" halibut. Unpublished. International Fisheries Commission. Dated September 1950.
Kramer, D.E. and B.C. Paust. 1985. Care of halibut aboard the fishing vessel. Alaska Sea Grant college program, marine advisory bulletin no. 18. 30p.
Mannan, A., D. I. Fraser, and W. J. Dyer. 1961. Proximate composition of Canadian Atlantic fish. J. Fish. Res. Bd. Canada (18), p 483-493.
Myhre, R. J. 1968? Observations on chalkiness of halibut caught by the trawler New Washington on goose Island ground in July, 1968. Unpublished. 4 pages. IPHC.
Patashnik, Max. 1965. The problem of chalky halibut. Unpublished release, Technological Laboratory, U.S. Bureau of Commercial Fisheries, Seattle, Wa. Dated Feb. 18, 1965.
Patashnik, M. and H. S. Groninger, Jr. 1964. Observations on the milky condition in some Pacific coast fishes. J. Fish. Res. Bd., Canada, 21(2), p 335-346.
Pegg, R. 1966. Personal communication from Ron Pegg, Memorial University of Newfoundland, to Steve Kaimmer, IPHC.
Stromme, G. 1996. Personal communication from Gail Stromme, quality assurance person for Sitka Sound Seafoods, to Sheri Gross. 5p.
Tarr, H. L. A., 1968. Postmortem degradation of glycogen and starch in fish muscle. J. Fish. Res. Bd. Canada, 25(8): 1539-1554.
Thompson, W. F. 1916. A note on a sporozoan parasite of the halibut. IN: report of the commissioner of fisheries for the year ending December 31rst, 1915. Victoria, BC. P. 127-129,
Tomlinson N., Geiger, S.E., and E. Dollinger. 1964. Chalky halibut. Fish. Res. Bd. Canada. Vanc. Lab. Circ. No. 33, 8p.
Tomlinson N., Geiger, S.E., and E. Dollinger. 1965. Chalkiness in halibut in relation to muscle pH and protein denaturation. J. Fish. Res. Bd., Canada, 22(3), p 653-663.
Tomlinson N., Geiger, S.E., and E. Dollinger. 1965. Free drip, flesh pH, and chalkiness in halibut. J. Fish. Res. Bd., Canada, 22(5), p 673-680.
Tomlinson N., Geiger, S.E., and E. Dollinger. 1966. Influence of fishing methods on the incidence of chalkiness in halibut. J. Fish. Res. Bd., Canada, 23(6), p 925-928.
Unk. 1996. Chalky halibut, the fish buyer’s nemesis. The Westcoast Fisherman, April 1996, p 21-22.