FACTORS AFFECTING COOKED TEXTURE QUALITY OF 



PACIFIC WHITING, MERLUCCIUS PRODUCTUS, FILLETS WITH 



PARTICULAR EMPHASIS ON THE EFFECTS OF INFECTION BY 



THE MYXOSPOREANS KUDOA PANIFORMIS AND K. THYRSITIS 



George Kudo, Harold J. Barnett, and Richard W. Nelson' 



ABSTRACT 



Pacific whiting is known to have abnormal cooked texture induced by enzymes of the Myxosporean 

 parasites Kudoa . An extensive United States-Canadian joint research project was initiated to explore 

 the correlation between texture quality and intensity of Kudoa infection. Enumeration of white and 

 black pseudocysts and identification of the Kudoa species present was done by the Canadian team 

 while texture quality was determined by the U.S. team. Data analysis showed that 1) white pseudo- 

 cysts were more closely correlated with cooked texture quality than were black pseudocysts; 2) K. 

 paniformis and mixed infections correlated well with sensory texture while K. thyrsitis infections 

 correlated poorly; 3) Pacific whiting from southern fishing areas had higher white pseudocyst counts 

 of K. paniformis and more soft abnormal texture than Pacific whiting from northern fishing areas; 

 4) nape and dorsal areas offish had higher intensities of Kudoa infections and greater incidences of 

 abnormal texture; 5) body length correlated weakly with texture quality, but there was no relation- 

 ship between sex and sensory texture. Results of experimental evaluations indicate that the visual 

 culling method may have some potential for use in sorting Pacific whiting with white and/or black 

 pseudocysts. However, the white pseudocysts require careful examination to be detected. Therefore, 

 a visual culling method may be too time consuming to be practical for use on a production line. 



Between 1982 and 1984, the annual catch of 

 Pacific whiting^, also known as Pacific hake, Mer- 

 luccius productus, harvested by American and 

 foreign fishing fleets in the territorial waters off 

 the Pacific coast of the United States, ranged be- 

 tween 80,000 and 100,000 t. Of this amount, be- 

 tween 67,000 and 79,000 t were annually har- 

 vested by a joint venture fishery with the Soviet 

 Union. The catch by other foreign countries, 

 mainly Poland and Bulgaria, operating in the di- 

 rected fisheries, ranged from 7,000 to 14,000 t"^. 

 Although the Pacific whiting resource has been 

 estimated to vary between 445,000 and 3,440,000 

 t (Dark 1985), its domestic use has been limited 

 because of soft texture associated with the pres- 

 ence of a parasitic Myxosporea of the genus 

 Kudoa . Patashnik et al. (1982) and Tsuyuki et al. 

 (1982) established that the flesh deterioration of 



'Utilization Research Division, Northwest and Alaska Fish- 

 eries Center, National Marine Fisheries Service, NOAA, 2725 

 Montlake Boulevard East, Seattle, WA 98112. 



2The U.S. Food and Drug Administration has ruled that this 

 species can be marketed as Pacific whiting (Robins et al. 1980). 



3W. Daspit, OFIS, Northwest and Alaska Fisheries Center, 

 National Marine Fisheries Service, NOAA, 7600 Sand Point 

 Way N.E., BIN C15700, Seattle, WA 98115, pers. commun. 

 March 1985. 



Manuscript accepted June 1987. 



FISHERY BULLETIN; VOL. 85, NO. 4, 1987. 



infected Pacific whiting was due to an enzyme- 

 induced proteolysis. However, the correlation be- 

 tween the degree of infection and the condition of 

 the flesh was not entirely clear. Sometimes 

 Pacific whiting heavily infected with the proto- 

 zoan parasite appeared, when cooked, not to be 

 affected, i.e., soft-textured, while lightly infected 

 fish had very poor textures. The discovery by 

 Kabata and Whitaker (1981) that Pacific whiting 

 is infected by two different species of Kudoa 

 (Fig. 1) explained some of these discrepancies. 

 Tsuyuki et al. (1982) found that these species, 

 Kudoa paniformis (Kabata and Whitaker 1981) 

 and Kudoa thyrsitis (Gilchrist 1924), differ from 

 each other in their enzyme activity, i.e., enzyme- 

 induced proteolysis. Because Pacific whiting can 

 be infected with one or both species oi Kudoa , the 

 final condition of the flesh might be determined 

 by the type o^ Kudoa since K . paniformis is capa- 

 ble of producing much heavier infections than K. 

 thyrsitis (Kabata and Whitaker 1981). 



From a public health standpoint, no protozoan 

 diseases of fish have been known to have man as 

 host (Oppenheimer 1962) and myxosporea per se 

 have never been reported to cause illness in hu- 

 mans (Konagaya 1982; Nagahisa et al. 1983). 

 Nonetheless, infection with Kudoa continues to 



745 



