Introduction:

Ichthyophonusis a cosmopolitan parasite of the class Mesomycetozoea that displays low host specificity ⁽¹⁾. It is an internal histozoic parasite that can be found in all visceral organs and the musculature of infected hosts, effects of infection vary greatly among individuals and host species⁽²⁾. Ichthyophonus infection does serious damage to culture fisheries because it causes a reduction of growth rates and death to fishes and hence, requires large expenditures for the sanitation of fish farms⁽³⁾.

This disease is chronic and lasts for up to a year or longer periods of time, most often affecting the well-vascularized organs of fish^(4,5). Ichthyophonus causes a systematic granulomatous infection in their hosts, produced infections in many different species of freshwater, estuarine, marine teleosts and adapt to a wide range of environmental conditions ⁽⁵⁾.

Received on 26.09.2015 Modified on 17.10.2015

Research J. Science and Tech. 7(4):Oct. – Dec. 2015; Page 234-237

DOI: 10.5958/2349-2988.2015.00034.0

Ichthyophonus has been reported from many temperate and some tropical waters ⁽⁶⁾. The aim of the present research is to reveal the histopathological changes in gill, liver and intestine of blue tilapia, O. aureus, collected from ponds of Marine Science Centre.The fish have been experimentally infected with fungi Ichthyophonus sp.

Material and Methods:

Experimental Fishes:

A total of 25 fish, blue tilapia were collected from ponds of Marine Science Centre during the period May to June 2014 and from September to December 2015. The samples were transferred in to glass basin (30×40×60) cm, distributed in 5 ponds, five fish samples in each pond to induce infections with one pond as a control. All samples were left for 15 days.

Fungal Isolation

The fungus Ichthyophonus sp. was isolated from the abdomen of blue tilapia, collected from the University of Basrah fish farm, and cultured in Potato Dextrose Agar (PDA) ⁽⁷⁾to preparation of fungal spore suspension. Spores broth was prepared according ⁽⁸⁾ and 10⁶ conc/ ml was selected by haemocytometer method, the broth was incubated at 4°C till use.

Inducing Ichthyophonus sp. Infection:

Blue tilapia was infected by the fungus Ichthyophonus sp. according method of ⁽⁹⁾. The infection was done by cutaneous scars on fish samples after doping it by 50 ml/ l metacaine methane sulphonate. Two ml of fungal broth were added to the fish ponds, after 15 days the histological tests of fish samples were done.

Histopathological Study

For histopathological study, the tissue specimens of gill, liver and intestine were excised, rinsed in normal saline and fixed in formalin buffer 10% for 24 h. After fixation, the tissues were dehydrated in an alcohol series of ascending concentration (70%, 80%, 90% and 100%, respectively), embedded in paraffin and sectioned at 5 µm. The tissue sections were stained with haematoxilin-eosin (H and E) and were examined by light microscope

RESULTS AND DISCUSSION:

In the present study observed Ichthyophonus sp. infects the gill, liver and intestine of blue tilapia. Behavioral signs, infected blue tilapia demonstrate decreased swimming performance, diseased individuals consume less food than uninfected group. Histopathological investigations have been carried out on infected gill, liver and intestine. In gill, hyperplasia, partial fusion of some lamellae and blood congestion. In liver, pathological changes in haepatopancreas tissues, focal necrosis, and fibrosis, infiltration and congestion. In intestine, swelling in lamina propria and fusion of villi and hemocyte infiltration (Figs 1-12(.

Fig. 1: Normal gill filaments of O. aureus (H and E, 400X), Sl: secondary lamella, Pc: filament epithelium.

Fig. 2: Gills of O. aureus infection with Ichthyophonus sp. (H and E, 400X), H: hyperplasia, F:fusion

Fig. 3: Gills of O. aureus infection with Ichthyophonus sp. (H and E, 400X), BC: blood congestion.

Fig. 4. Normal histological of liver tissue of O. aureus (H and E, ×400).

Fig. 5: Haepatopancreas tissues of O. aureus infection with Ichthyophonus sp. (H and E, 400X), N: focal necrosis.

Fig. 6: Haepatopancreas tissues of O. aureus infection with Ichthyophonus sp. (H and E, 400X), C: congestion.

Fig. 7: Haepatopancreas tissues of O. aureus infection with Ichthyophonus sp. (H and E, 400X), F: fibrosis.

Fig. 8: Haepatopancreas tissues of O. aureus infection with Ichthyophonus sp. (H and E, 400X), C: congestion, IN: infiltration and congestion.

Fig. 9: Normal histological of intestine tissue of O. aureus (H and E, ×400).

Fig. 10: Intestine tissue of O. aureus infection with Ichthyophonus sp. (H and E, ×400), H: hemocyte infiltration.

Fig. 11: Intestine tissue of O. aureus infection with Ichthyophonus sp. (H and E, ×400), SL: swelling in lamina propria.

Fig. 12: Intestine tissue of O. aureus infection with Ichthyophonus sp. (H and E, ×400), FV: fusion of villi.

The pathological consequences of fungi effects on fishes are well documented and serve as an evident to support the view that fungi are one of the main causes of mortality in population of fish. Different species of fungi, therefore pose serious threat to the fishes, with the invasion of a fish by fungi an infection develops in the host ⁽^1,10⁾.

The present study observed may be due to the fungi adhesions which make a mechanical damage in the gill, liver and intestine and make this histopathological change. Obviously, severity of lesions that induced by the fungi in the host tissue depends mainly on the fungi morphology ⁽¹¹⁾. Severe alterations of gills might be negatively affected on the respiratory process of the fish. Also, discussed that, gill fungi are pathogenic in massive infestations because they damage the epithelia and cause secretion excessive amount of mucus which affects respiration^(10,6⁾.

However, the extent of damage or pathogenic condition depends on fungi species and the site where they localize in the host^(6,11,12). ⁽¹²⁾ studied the histopathological changes in the liver, heart, spleen kidney and intestine of yellowtail flounder, a trial experiment five yellowtail flounder were necropsied 127 days after being injected with 1000 spores of I. hoferi collected from diseased wild yellowtail flounder, all fish showed lesions on the liver, heart, spleen kidney and intestine identical to lesions in infected wild –yellowtail. Chronic infection was associated with levels of enzootic prevalence less than 1% with progressive connective tissue encapsulation of the Ichthyophonus spores ⁽¹³⁾. Even in the chronic condition, infection was rarely fully controlled by the host and deaths occurred within six months, acute infections were noted as severe tissue invasion and necrosis leading to death within 30 days and was usually associated with epizootic mortality events ⁽¹²^,6⁾. The level of tissue damage observed in combination with no visual evidence of recovery from Ichthyophonus leaves little doubt that this infection is lethal in yellowtail flounder. However time until death and the timeline for disease progression have not been demonstrated for yellowtail flounder.

Conclusion:

Pathogenicity is believed to vary according to host species, environmental conditions and the species of Ichthyophonus.

REFERENCES:

1- Kramer-Schadt, S.; Holst, J.C. and Skagen, D. Analysis of variables associated with the Ichthyophonus hoferi epizootics in Norwegian spring spawning herring, 1992-2008. Can. J. Fish. Aquat. Sci.67, 2010: 1862-1873.

2- Legault, C.M.; Alade, L.; Gross, W.E. and Stone, H.H. Stock assessment of Georges Bank yellowtail flounder in 2013. TRAC Working Paper 2013/ 138p, 2013.

3- Oskarsson, G. and J. Pallson. The Ichthyohponus hoferi outbreak in Icelandic summer-spawning herring stocks during the autumns 2008 to 2010. ICES WRKBND 2, 2011.

4- Kocan, R.M. Proposed changes to the nomenclature of Ichthyophonus sp. life-stages and structures. J. Parasitol. 99, 2013: 906-909.

5- Zadeh, M.J.; Peyghan, R. and Manavi, S.E. The Detection of Ichthyophonus hoferi in naturally infected fresh water Ornamental fishes. J. Aquac. Res. Development. 5, 2014: 289.

6- Fafioye, O.O.; Efuntoye, M.O. and Osho, A. Studies on the fungal infestation of five traditionally smoke-dried freshwater fish in Ago-Iwoye, Nigeria. Mycopathologia. 154(4), 2002: 177-9.

7- McGinnis, M.R. Laboratory hand book of medical Mycology. Acad. Press, New York, 1980: 66 pp.

8- Fregeneda Grandes, J.M.; Fernandez Diez, M. and Aller Gancedo, J.M. Experimental pathogenicity in rainbow trout Oncorhynchus mykiss (Walbaum), of two distinct morphtypes of long-spined Saprolegnia isolates obtained from wild brown trout, Salmo trutta L., and river water. J. Fish Dis. 24, 2001: 351-359.

9- Dykstra, C.L.; Williams, G.H. and Gregg, J. Ichthyophonus prevalence in Pacific halibut – a pilot study. Int. Pac. Halibut Comm. Report of Assessment and Research Activities 2011. 445-452. 2012.

10- Vollenweider, J.J.; Gregg, J.L.; Heintz, R.A. and Hershberger, P.K. Energetic cost of Ichthyophonus infection in juvenile Pacific herring (Clupeapallasii). J. Parasitol. Res., 2011, Article ID 926815, 10 pages.

11- Carl, H. and Roxanna, S. Prevalence of Ichthyophonus sp. in yellowtail flounder sampled during the seasonal bycatch survey on Georges Bank. Fisheries and Oceans Canada, TRAC, 2014 http://www.nefsc.noaa.gov/TRAC-Public/31.

12- Kocan, R.; P. Hershberger, G.S. and J. Winton. Effects of temperature on disease progession and swimming stamina in Ichthyophonus-infected rainbow trout, Oncorhynchus mykiss (Walbaum). J. Fish Dis. 32, 2009: 835-843.

Received on 26.07.2015 Modified on 10.08.2015

Research J. Science and Tech. 7(4):Oct. – Dec. 2015; Page 230-233

DOI: 10.5958/2349-2988.2015.00033.9