Occurrence of 'soft flesh' condition induced by Kudoa thyrsites parasite in the Iberian European sardine stock

Abstract

European sardine Sardina pilchardus is a commercially valuable coastal pelagic fish species. Spain is one of the largest sardine suppliers in Europe and the Iberian stock is of particular significance. Kudoa parasites are known to infect sardines causing the so-called 'soft flesh' condition; however, data on the occurrence of 'soft flesh' in this sardine stock are limited. This study investigates the occurrence of Kudoa-induced 'soft flesh' in the Iberian sardine stock caught in 2023 off the northern Spanish Atlantic coast (Division 8.c). Five hundred specimens were examined for 'soft flesh' by manual texture testing and visual inspection 48 h post-catch using standardized procedures. 'Soft flesh' was detected in 5.4% (27/500) of the sardines. Microscopic examination of muscle samples revealed the presence of Kudoa thyrsites-like myxospores in all 'soft flesh'-affected fish, which based on SSU rDNA gene sequence analysis was identified as K. thyrsites. The unsightly appearance of infected fillets represents a substantial food quality issue for the Iberian sardine stock that could reduce marketability and consumer confidence in both local and international markets. This is particularly relevant since larger Iberian sardines, which are highly appreciated by consumers, appear to be the most affected.

Keywords: Kudoa thyrsites; European sardine; Iberian sardine stock; Quality reducing parasite; Spanish fishery; ‘Soft flesh’.

Fig. 1

Illustration of Kudoa-induced ‘soft flesh’ condition in Iberian sardines from off the northern Spanish Atlantic coast (Cantabrian Sea) (ICES division 8.c.)

Fig. 2

Spores of K. thyrsites–like morphotype from Iberian sardine