Title : Parasites hazardous to the health of commercially important fish species in the Black Sea and the Sea of Azov
Abstract:
Between 2011 and 2017, we identified the microsporidian Loma acerinae (Jirovec, 1930) Lom & Pekkarinen, 1999 in the Karkinit Bay (Black Sea) and the Sivash Bay (the Sea of Azov), infecting six fish species belonging to the families Gobiidae (Neogobius melanostomus, N. fluviatilis, Ponticola eurycephalus, Gobius ophiocephalus, Proterorhinus marmoratus) and Atherinidae (Atherina boyeri). In the vicinity of Odessa and Ochakov, the parasite has been documented in N. melanostomus, N. fluviatilis and Proterorhinus semilunaris (Ovcharenko et al., 2017). According to our data, the intensity of infection in the intestine reached as many as 256 parasite cysts in G. ophiocephalus and over 1,000 cysts in N. fluviatilis and N. melanostomus –levels that inevitably impaired normal intestinal function (Yurakhno, 2018).
According to our data from 2011 – 2014, the coccidian Eimeria merlangi Zaika, 1966, found in the gallbladder of the Black Sea whiting Merlangius merlangus (Gadidae), reached high levels of infection intensity. This was accompanied by petechial hemorrhages in the gallbladder wall, causing both the wall and the contents of the gallbladder – while remaining transparent – to take on a distinct reddish hue (Yurakhno, 2018).
The testes of the Sprattus sprattus (Clupeidae), were found to be infected with the coccidian Eimeria sardinae (Thélohan, 1890) Reichenow, 1921. According to our data from 1998 – 2000, E. sardinae was present along the Crimean coast – from Yevpatoria to Kerch – with an infection intensity ranging from tens to hundreds or even thousands of oocysts per fish testis (Yurakhno & Gaevskaya, 2002, 2004). We observed that, at high levels of infection intensity, the sprats' testes resembled ovaries filled with eggs; furthermore, the weight of such testes was lower than that of uninfected ones. We did not observe the complete castration of the host – a phenomenon known to occur in other clupeid fish due to this parasite – because the parasite’s mass sporulation took place during the post-spawning period (Yurakhno, 2018).
In the Black Sea and the Sea of Azov 16 species of gobiid fish serve as hosts for the myxosporean Kudoa nova Naidenova, 1975 N. melanostomus, N. fluviatilis, Proterorhinus marmoratus, Mesogobius batrachocephalus, Gobius niger, G. ?phiocephalus, Gobius cobitis, Knipowitschia longicaudata, Pomatoschistus microps, P. minutus, Ponticola cephalargoides, P. eurycephalus, P. platyrostris, P. ratan, P. syrman, Tridentiger trigonocephalus. We have been studying this species since 1989 across various regions of this basin. In the muscles of heavily infected fish, a decrease in protein and fat content – by 3.7 % and 0.16 %, respectively – was observed, along with a reduction in saturated and unsaturated fatty acids, contrasted by an increase in polyunsaturated fatty acids. Furthermore, the relative biological value of minced meat derived from round goby specimens infected with Kudoa nova was found to be 10.9 % to 18.9 % lower than that of the control group (Gorchanok, 2008).
The myxosporeans Myxidium gadi Georgevitsch, 1916 and Ceratomyxa merlangi Zaika, 1966, found in the gall bladder of the Black Sea whiting Merlangius merlangus (Gadidae), as well as Ceratomyxa elegans Jameson, 1929, found in the gall bladder of Scorpaena porcus (Scorpaenidae), can cause a thickening of the gall bladder walls, a change in color from green to white or yellowish-white, and the complete replacement of bile with a the-like mass consisting of the parasite’s plasmodia and spores. A biochemical analysis of the lipid composition in the muscles and liver of whiting with heavy or light M. gadi infections revealed no changes in the muscles; however, in the liver, there was a 2 – 3-fold decrease in total lipids and a 3 – 4-fold decrease in triacylglycerols – but only in males. This was not observed in the livers of females (Shchepkina, Yurakhno, 2002, 2003, 2004, 2008; Yurakhno, Shchepkina, 2004). We observed a significant decrease in the spleen index and an increase in the liver index in infected individuals. Differences were also identified in the parameters of the antioxidant enzyme system in the livers of fish from different groups. Specifically, the activity of catalase and superoxide dismutase was reduced in fish with moderate levels of infection, while glutathione reductase activity was lower in individuals with moderate to high infection intensities compared to the control group (Skuratovskaya et al., 2010, 2011, 2012, 2013).
A high level of infection in Engraulis encrasicolus (Engraulidae) with larvae of the nematode Hysterothylacium aduncum (Rudolphi, 1802) Deardorff & Overstreet, 1981, and in Neogobius melanostomus (Gobiidae) with metacercariae of the trematode Cryptocotyle concavum, leads to a sharp reduction in their lipid reserves. In heavily infected E. encrasicolus lipid reserves decrease by 15 – 36 % in red muscle, 33 – 71 % in white muscle, and 28 – 63 % in the liver. In N. melanostomus these values ??show a decrease of 30 – 71 % in the liver and 37 – 57 % in the muscles (Shchepkina, 1980).
In Scophthalmus maeoticus (Scophthalmidae) infected in the intestine by the cestode Bothriocephalus gregarius (Renaud, Gabrion & Pasteur, 1983) superoxide dismutase activity in the muscles is 1.5 times higher, while catalase activity is reduced by half. In the liver of heavily infected turbot, superoxide dismutase activity is 5 times higher, and peroxidase levels are also elevated (Rudneva et al., 2004).
In our study biochemical response of two fish species of Gobiidae – Gobius ophiocephalus and Ponticola eurycephalus to Cryptocotyle spp. metacercariae infection (Trematoda) at the mouth of River Chernaya (Sevastopol, Black Sea) was investigated in September 2012, 2013. In muscle samples of P. eurycephalus glutathione-S-transferase activity was significantly lower in the specimens with high intensity of infection (III group) than that of non-infected ones (Group I). On the other hand, thiobarbituric acid-reactive substances concentration in individuals from Group III was significantly higher when compared with the values of fish from groups I and II (with middle level of infection). In muscle samples of G. ophiocephalus superoxide dismutase and catalase activities were significantly higher in fish from Group III than those of Group I and II and a similar result was obtained in glutathione reductase activity in specimens from Group III when compared with Group I (Skuratovskaya et al., 2020).
This work is supported within the framework of the IBSS state research assignment Biodiversity as the basis for the sustainable functioning of marine ecosystems, criteria and scientific principles for its conservation (No. 124022400148-4) (Russian Federation).
