Anisakis Infection in the Spotted Flounder Citharus linguatula (Pleuronectiformes: Citharidae) Caught in the Gulf of Cadiz (Area FAO 27-ICES IXa) Appears to Negatively Affect Fish Growth

Abstract

Spotted flounder (Citharus linguatula L.) caught in the Gulf of Cadiz (area FAO 27 ICES IXa) were examined for Anisakis larvae and to assess the possible risk of anisakiasis in humans through consumption of this fish. Larvae of the genera Anisakis and Hysterothylacium were identified in the analysis of 128 purchased fish specimens. All Anisakis larvae corresponded to type I. Molecular analysis showed the presence of A. pegreffii, A. simplex s.s., and recombinant genotype between the two. The prevalence of Anisakis was 9.4% with a mean intensity of 1.42, while for Hysterothylacium the values were 12.5% and 1.06. The length and weight of the fish, but not Fulton's condition factor, varied significantly between infected and uninfected fish. The prevalence of Anisakis increased with fish length, with no fish parasitized with Anisakis measuring less than 15.5 cm (2-2.5 years old), which is probably related to the reported dietary change of these fish at around 2 years of age. Fish not parasitized with any of these nematodes showed positive allometric growth, while those parasitized only with Anisakis showed negative allometric growth. When comparing both groups including only fish ≥ 15.5 cm (the smallest size of Anisakis-infected fish), the difference is shown to be statistically significant (p = 0.01), suggesting that Anisakis infection of spotted flounder negatively affects fish growth even when parasite intensity is low, which may have important economic repercussions. Finally, the low prevalence and, above all, intensity of Anisakis in these fish, as well as the habit of consuming this fish fried in oil in our geographical area, means that the risk of acquiring anisakiasis through consumption of this fish is low.

Keywords: Anisakis; Citharus linguatula; FAO 27.IXa; Gulf of Cadiz; Hysterothylacium; Spain; anisakiasis; fish growth; spotted flounder.

Figure 1

Potential weight–length relationship (y = a·x^b) in non-Anisakis-infected fish (n = 101; circle) and Anisakis-infected Citharus linguatula (n = 12; square). Fish parasitized only with Hysterothylacium have been excluded. Uninfected ± SD: exponent b ± 0.0731, coefficient a ± 0.0006. Infected ± SD: exponent b ± 0.3340, coefficient a ± 0.0152.

Figure 2

Logarithmic transformation of the relationship between weight and length of Anisakis-infected (n = 12; square) and non-Anisakis-infected Citharus linguatula (n = 41; circle), considering only individuals ≥ 15.5 cm (the length of the smallest Anisakis-infected fish). Fish parasitized only with Hysterothylacium have been excluded. ANCOVA statistical comparison shows that the curves are significantly different (p = 0.01). The value of b corresponds to the slope of the line.

Figure 3

Relationship between mean length of uninfected Citharus linguatula length classes (<12 cm with 8 fish, 12–12.9 with 6, 13–13.9 with 16, 14–14.9 with 16, 15–15.9 with 24, 16–16.9 with 19, and ≥17 cm with 12 fish) and Fulton’s condition factor.

Figure 4

Prevalence of Anisakis and Hysterothylacium in Citharus linguatula by length class. The number of fish per length class, from left to right, are: 14, 17, 20, 28, 26, and 22.