review of Kudoa-induced myoliquefaction of marine fish species in South Africa and other countries

Abstract

Myoliquefaction of fish musculature results in customer quality complaints and in huge economic losses, especially with regard to Pacific hake (Merluccius productus), farm-reared Atlantic salmon (Salmo salar), South African pilchards (Sardinops ocellatus) and Cape snoek (Thyrsites atun). Myoliquefaction, or 'jelly flesh', is caused by proteolytic enzymes released by the marine myxosporean parasite, Kudoa thyrsites, after the death of the fish. Currently there are no fast methods of detection for this microscopic parasite, and because myoliquefaction is evident only after 38-56 h post-mortem, infected fish inevitably reach the processor and/or consumer. Several methods of detection have been investigated, but most of these methods are time-consuming and/or result in destruction of the fish, and are thus impractical for fishing vessels and fish processors. Limited research is available on possible means of destroying or inhibiting the post-mortem activity of the parasitic proteolytic enzyme. Means such as manipulating post-mortem pH and temperature control have been suggested; leaving opportunities for research into food technology applications such as cold-chain management and ionising radiation. Myoliquefaction in marine fish in South Africa and other countries Myoliquefaction is a common phenomenon in South African Cape snoek (Thyrsites atun). The musculature of infected fish becomes completely soft and jelly-like (Figure 1) and is commonly known as 'pap snoek'. Soft flesh was described for the first time in T. atun in Australia and South Africa as early as 1910 and 1924, respectively. 13 Myoliquefaction in Cape snoek is caused by the myxosporean parasite K. thyrsites. This parasite was shown to have infected up to 27 fish species worldwide 11 , including mahi-mahi (Coryphaena hippurus) 14 , Atlantic salmon and Pacific hake 3,10,11. South African pilchard (Sardinops ocellatus), Cape hake (Merluccius capensis) and Cape dory (Zeus capensis) are also known to be infected by K. thyrsites (Table 1), with pilchards being among the most heavily infected fish species in South African waters. 15 The presence of K. thyrsites, associated with myoliquefaction in dried fillets exported to Japan, was reported for the first time in 2005 in splendid alfonso (Beryx splendens) from South Africa. 16 In the Northwest Pacific of North America, the occurrence of K. thyrsites is of great economic importance as it has a significant impact on farmed Atlantic salmon and, to a lesser extent, in coho salmon (Oncorhynchus kisutch). 17 Kudoa paniformis often occurs simultaneously with K. thyrsites in Pacific hake. 18 South African hake 19 is believed to undergo accelerated myoliquefaction because K. paniformis produces both acidic and neutral proteolytic enzymes 19 ; K. thyrsites only produces acidic enzymes 1. Several studies 2,20,21 have indicated that the optimum conditions for endogenous enzymes from K. paniformis in Pacific hake are a pH range of 5.25-5.50 and a temperature range of 52-55 °C.

Infection of the muscle tissue of the filter-feeding cichlid, Chaetobranchopsis orbicularis Steindachner, 1875, by Kudoa orbicularis (Myxozoa: Multivalvulidae) on Marajó Island in the Brazilian Amazon region

“…Progressive softening of the muscles was observed during necropsy, indicating rapid enzymatic autolysis, as noted by Henning et al (2013) in specimens infected by Kudoa, who identified the rapid softening of the muscle, which led to post mortem myoliquefaction, as an enzymatic process. However, Andrada et al (2005) and Azevedo et al (2016) did not observe any evidence of myoliquefaction in the specimens they examined.…”

Marine fish parasitology in South Africa: history of discovery and future direction

“…Once infected, the flesh of the fish becomes soft and liquefies (myoliquefaction) causing a condition termed 'pap snoek' by the locals. Today K. thyrsites is considered to be a parasite with a worldwide distribution, infecting a wide range of host species and is responsible for significant economic losses to the fishery sector (Henning et al 2013). …”

Myxosporean parasites of marine fishes: their distribution in the world's oceans

“…In addition, some histozoic species are important as spoilage agents because they produce unsightly macroscopic cysts in the fish flesh and/or cause the condition known as post-mortem myoliquefaction, resulting in considerable economic losses (Henning et al 2013). They have also been used as biological tags in population studies of commercially important species of marine fish (Kabata, 1967;Khan and Tuck, 1995;Larsen et al 1997;Campbell, 2005).…”