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The relationship between growth rate and ossification is not consistent among fish. In some species, fast-growing individuals ossify earlier, while in other species, a trade-off between growth rate and ossification exists. This research was conducted to test the hypothesis about the existence of a trade-off mechanism in common carp offspring. For this purpose, specimens from two groups of common carp offspring (96 in total) with different growth rates were sampled at multiple time points between 5 and 29 days post-hatching. The standard length was measured and presented in correlation with the days post-hatching. To evaluate the skeletal system development, whole specimens were fixed in 10% neutral buffered formalin and stained for bone and cartilage. Particular emphasis was placed on the onset of ossification in the clearly visible bones of the head, vertebral column, and fins. According to our findings, larger, fast- growing specimens ossify earlier. The hypothesis on the existence of a trade-off between fast growth and the onset of ossification in common carp was not confirmed in our study., Odnos između brzine rasta i procesa okoštavanja u riba nije ujednačen. U nekih vrsta te su vrijednosti u pozitivnoj korelaciji, dok je u drugih vrsta prisutan svojevrsni kompromis (engl. trade-off), brži rast negativno utječe na proces okoštavanja. Cilj ovog istraživanja je provjeriti hipotezu o postojanju negativne korelacije između brzine rasta i procesa okoštavanja u šarana (Cyprinus carpio). U tu svrhu, jedinke šarana podrijetlom iz dvije skupine s različitom brzinom rasta (ukupno 96 jedinki) uzorkovane su između 5. i 29. dana nakon valjenja. Mjerena je standardna dužina i prikazana u korelaciji s brojem dana poslije valjenja. U svrhu procjene razvoja koštanog sustava, uzorci su fiksirani u 10% neutralnom formalinu i obojeni metodom za prikaz kosti i hrskavice. Poseban naglasak stavljen je na proces okoštavanja u jasno vidljivim kostima glave, kralježnice i peraja. Prema rezultatima našeg istraživanja, u brzorastućih jedinki proces okoštavanja je nastupio ranije. U ovom radu opovrgnuta je hipoteza o postojanju negativne korelacije između brzine rasta i procesa okoštavanja.

This report describes a peripheral nerve sheath tumour in 8 European eels Anguilla anguilla L. from a fish farm located in Croatia. The newborn tissue appeared as smooth and soft skin nodules without pronounced colour change. Nodules were dome-shaped with a pale crater and were present on different body areas. In general, nodules were located as series of differently sized protrusions extending along the lateral line on both sides of the fish, as well as sensory canals on the head. Cut sections showed a homogeneous, pale white-grey texture. Histologically, the pathological tissue was located in the dermis, occasionally intruding into the hypodermis, and pushing as a space-occupying mass against the underlying muscle tissue without any evident boundaries. The pressure also caused changes in the overlying epidermis, such as atrophy, spongiosis and erosion. In some areas, the epidermis was 1 cell thick and club and goblet cells had completely disappeared. Ultimately, these changes resulted in shallow ulceration. Tumour tissue was characterized by a scant population of spindle or stellate cells, with oval, hyperchromatic nuclei and pale cytoplasm embedded in a copious myxoid matrix. Cells were arranged in fascicles and whorls, extending in a poorly defined manner among the dermal collagen bundles. Occasionally, adipose cells were also detected, mainly in the central portion of the bulges. Myxoid areas appeared rich in metachromatic and alcianophilic mucous ground substance. Reticular fibres and collagenous connective tissue were scarce. Immunohistochemistry (IHC) using antibodies against S-100 and glial fibrillary acidic protein caused a slight positive reaction in neoplastic dendritic cells. High magnification showed the immunostaining to be cytoplasmic in all tumour cells. IHC with anti-calretinin antibody gave only negative results. Macroscopic, histological, histochemical and immunohistochemical findings were consistent with a diagnosis of multicentric myxoma of the dermal nerve sheaths, a tumour not yet reported in fish.

This study extends the original description of Eimeria dicentrarchi Daoudi and Marquès, 1987, a common coccidian parasite of European sea bass from the mid-eastern Adriatic, by providing insights into the parasite’s site of infection, development and pathogenicity. E. dicentrarchi was found in various developmental stages in most segments, mainly anterior, of the digestive tract. In infected segments of the digestive tract, merogonic and gamogonic stages were located in the enterocyte cytoplasm, whereas sporogonic stages were situated in the epithelium and occasionally beneath it, in the lamina propria. Most oocysts in the lumen of the digestive tract were completely sporulated, indicating endogenous sporulation. E. dicentrarchi infection caused localised histopathological changes, restricted primarily to individual epithelial cells. Additionally, the results of our preliminary study suggest that oral administration of potentiated sulphonamide Trimetosul® (trimethoprim-sulfadiazine) may be effective against E. dicentrarchi infection., Ovo istraživanje doprinosi izvornom opisu kokcidije Eimeria dicentrarchi Daoudi i Marquès, 1987, koja se učestalo pojavljuje u lubina u istočnom dijelu srednjeg Jadrana. U radu je prikazan njezin smještaj u probavnoj cijevi, razvojni ciklus i patološki učinak na domaćina. Prisutnost razvojnih stadija E. dicentrarchi utvrđena je u raznim dijelovima probavne cijevi, uglavnom u prednjem dijelu crijeva. Čitav razvojni ciklus odvija se u citoplazmi enterocita, iako do sporogonije dolazi i u lamini propriji. Oociste većinom potpuno sporuliraju u probavnoj cijevi što upućuje na unutarnju sporulaciju. E. dicentrarchi uzrokuje lokalizirane histopatološke promjene primarno ograničene na pojedinačne epitelne stanice. Rezultati preliminarnog istraživanja pokazuju da potencirani sulfonamid Trimetosul® (trimetoprim-sulfadiazin) može biti učinkovit u liječenju invazije kokcidijom E. dicentrarchi.

This study presents data on the pathogenic effect of a non-native cestode, Atractolytocestus huronensis (Caryophyllidea), on common carp cultured at a fish farm in Croatia. Histopathological examination revealed that A. huronensis causes only local damage within the infected part of the intestine. No differences were observed in the pathological effect of the tapeworm on fish of different age classes. In the farm studied, no mortalities or increased losses during wintertime were observed. The cestode was found in all examined age classes (i.e. carp fry, one-year old and two-year old carp), and the intensity of infection ranged from 1 to 183 parasites per fish (mostly 4 to 9). The highest prevalence was observed during August in both one- and two-year old carp, with an absence of parasites in April and during the winter period (end of December)., U radu je prikazan patološki učinak trakavice Atractolytocestus huronensis (Caryophyllidea) na šarana, podrijetlom s ribnjačarstva smještenog u Republici Hrvatskoj. Histopatološki nalaz pokazao je da, neovisno o uzrasnoj skupini šarana, Atractolytocestus huronensis uzrokuje samo ograničena oštećenja na mjestu prihvaćanja. Kao posljedica nametničke invazije, nisu utvrđena uginuća niti povećani gubitci tijekom zime. Prisutnost trakavice utvrđena je u svim pregledanim uzrasnim skupinama (mladunci, jednogodišnji i dvogodišnji mlađ) s jačinom invazije od 1 do 183 nametnika po domaćinu (najčešće od 4 do 9). Najviša prevalencija kod jednogodišnjega i dvogodišnjega mlađa utvrđena je u kolovozu, dok u travnju i tijekom zime (kraj prosinca) trakavica nije pronađena.