The impact of co-infection of sea lice and its concurrent some bacterial diseases with field treatment trials in some marine cultured fishes

Co-infection is frequently found between sea lice and other pathogens, with high prevalence in the field and is highly detrimental to fish health. In this study, a total of 100 sea bass (Dicentrarchus labrax) were collected from a private marine farm that suffered from severe co-infection. All fish were examined for bacteriological and parasitological infections with trials for treatment. The detected pathogens among the examined D. labrax were V. alginolyticus (80%) and sea lice, Caligus minimus (100%). The clinical pictures showing dark skin coloration, excess mucus secretion, and detached scales with sever hemorrhage at fins and the operculum. The internal organs showed congestion and hemorrhages with small grossly ascetic fluid in the abdominal cavity. Water samples were analyzed for confirmation of normal condition and all physicochemical parameters were within the normal ranges in the marine fish farm. The antibiotic susceptibility against 11 antibiotics was tested and V. alginolyticus sensitive to ciprofloxacin and Trimethoprim /Sulfamethoxazole. The naturally infected fish could be treated successfully by Malathion in a single dose (0.1 mg/L for 30 minutes) as a short duration bath and then fed a ration containing  Ciprofloxacin (150 mg / Kg body wt.) for ten days.  The mortality rate declined, the clinical signs disappeared and the fish returned to a normal state of health. Co-infections have a fundamental effect and can alter the course and the severity of different fish diseases. Co-infection (bacterial and parasitic diseases) need further studies by conducting more experiments in the fish farm and using modern and fast diagnostic methods to control these diseases.