The Fish Pathology Group is specially focused on studies involving fish infections by Myxozoa, Coccidia, Monogenea and Scuticociliatidia parasites. Specifically, we have been involved in several National and International research programs dealing with pathological, epidemiological, and immunological aspects of these fish parasitoses. Aspects like in vitro cultivation and antigenic characterisation of the parasites, evaluation and modulation of fish innate and adaptive immune responses, or histopathology and pathogenic mechanisms, are among our primary research lines. We try to keep an equilibrium between applied research (development of validated diagnostic tests, treatments, immunoprophylaxis) and more basic research (life cycles, molecular phylogeny and taxonomy). In addition, we offer diagnostic services and consulting in fish health, as well as scientific coordination in joint private-public research programmes.

We have ongoing projects and contracts studying different parasitic problems affecting cultured fish, focused in the following organisms:

MYXOZOA: We have described several new myxozoan species such as Sphaerospora dicentrarchi, Sphaerospora testicularis, Ceratomyxa sparusaurati, Ceratomyxa labracis, Ceratomyxa diplodae, Zschokkella mugilis, Polysporoplasma  (now Sphaerospora) sparis and Polysporoplasma (now Sphaerospora) mugilis.

More recently we have described the new myxozoan genus Enteromyxum, which present interesting biological features such as direct, spontaneous fish-to-fish transmission, as well as a wide host spectrum and very high pathogenicity. The turbot myxozoan Enteromyxum scophthalmi, and Enteromyxum leei (formerly Myxidium leei) of sparids and other Mediterranean fish are the main studied species. We cover aspects of the life cycle and epidemiology, and we have developed and validated PCR diagnostic tests useful for large-scale epidemiological surveys of wild and cultured fish, as well as putative invertebrate hosts. The study of pathogenesis and host mechanisms of resistance to the infections is oriented to the control of these important infections through immunomodulation or selections of resistant fish families. Part of these studies have been framed in the EU-funded research project MYXFISHCONTROL (QLRT-2001-00722),  and the Spanish projects EnteromyxControl-AGL2009-13282-C02-01 and Mi2Fish (AGL-2013-48560-C02-2-R). The most recent work on these myxozoans is currently underway is the H2020 project ParaFishControl.

Enteromyxum leei fresh smear of a primary cell harbouring two spores and one accompayning cell.

We are core and active members of the Myxozoan Network, established during the EAFP conference at Malta in 2003. Have a look at our Myxozoan Publication Section.

From left to right: Dr. J.L. Bartholomew, Dr. A. Diamant, Dr. O. Palenzuela, Dr. A. Sitjà-Bobadilla, Dr. M. El-Matbouli, Dr. S.W. Feist.

CILIATES: Infections by an Uronema-like scuticociliate (Philasterides dicentrarchi according to some authors) are among the most serious current parasitic threats for turbot cultivation. The studies in our laboratory are aimed to the characterisation of different strains, the evaluation of their virulence, and the development of a first generation of imunoprophylaxis strategies based on live-attenuated, or killed ciliate strains. We keep several stains of fish scuticociliates in vitro in our facilities.

Have a look at our “Other Pathogens” Publication Section.

Philasterides dicentrarchi image at SEM

APICOMPLEXA:  We have described several new apicomplexan species such as Eimeria sparis, Goussia sparis, Cryptosporidium molnari and Cryptosporidium scophthalmi. Infections by Cryptosporidium are not usually considered a primary, serious threat for fish aquaculture. However, in previous studies a high prevalence and intensity has been found in some lots of juvenile sea bass, sea bream (C. molnari) and turbot (C. scophthalmi). Such a parasite load could result in a factor of further stress or immunodepression of fish in a very critical phase of culture, and the true pathogenic role of this parasites might be underestimated. We have studied the interaction and synergistic effects of parasites like Cryptosporidium with several opportunistic bacteria and parasites. Furthermore, most piscine Cryptosporidium spp. have not yet been characterised at the molecular level. We have conducted molecular phylogeny studies on Cryptosporidium molnari, in order to compare fish cryptosporidia with species infecting other vertebrates, including C. parvum.

Have a look at our Coccidian Publication section.

Fresh smear of stomach with groups of oocysts of C. molnari.

MICROSPORIDIA: The new species Enterospora nucleophila, described in 2014 in collaboration with Professor Ann Cali (Rutgers University, USA), is an intranuclear parasite located at the intestine of gilthead sea bream. It is considered and emerging pathogen in Mediterranean aquaculture an produces a serious emaciative disease. We are currently working on its epidemiology, transmission and development of diagnostic tools.

Gilthead sea bream juvenile (bottom) seriously affected by E. nucleophila.

MONOGENEA: The monogenean Sparicotyle chrysophrii (Microcotylidae) is one of the most insidious pest in gilthead sea bream culture throughout the Spanish Mediterranean coast. The large size of the haematophagous adults, and their anchorage structures result in gill erosion and damage, serious anaemia, lethargy, respiratory stress and enhanced susceptibility to secondary, opportunistic infections. In some farms, infections are established almost year-round, and only frequent net changes can keep the infections to low-level dropping mortality. We have studied aspects such as the epidemiology and pathology of the infections, the interactions with other parasites and bacteria and, more specifically, the effect of Praziquantel as a possible therapy for the control of these infections. We are conducted experiments to determine the effect on the haematology of the fish and the possible beneficial effect of some feed additives.

Have a look at our Other Pathogens and Diseases Publication Section.

Eggs of S. chrysophrii from a gill fresh smear

IMMUNE AND DIET RELATED STUDIES: In the recent years, we have also established a research line to evaluate the effects of fish feed and additives on the immune system of fish and their susceptibility to diseases, in the framework of different European projects (AQUAMAX, AQUAEXCEL, ARRAINA) and contracts with companies like NOVUS International, SKRETTING or NOREL.

Have a look at the results in the Immunology and Nutrition Publication Section.

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