Fisheries play an important role in increasing the Nepalese economy as well as sustaining livelihood of some ethnic groups of our country. With the increased demand of fish, pisciculture have also increased to a great extend. Due to the rise in fish culture, there has been also rise in fish diseases. The study aims to investigate different parasitic, bacterial, fungal diseases in fish and to suggest treatment to control the diseases in four different fish farm of Nepal. A cross- sectional qualitative method was used to collect data from four selected fish farm (Kakani, Trishuli, Begnas, Mirmi) of Nepal. Infected fishes were transferred to the lab in oxygen filled plastic bags and further tested for bacterial, fungal and parasitic infection. The result of the study indicates that Epizootic Ulcerative Syndrome was the most common bacterial-fungal disease that had a significant impact on common carp fish especially in Trishuli, Begnas and Mirmi. Coccidiosis caused by Eimeria spp was found to be a growing problem in rainbow trout farming (Kakani, Nuwakot) infecting intestine, liver, gut and skin causing yellow diarrhea and skin lesions. Trichodina was observed number one problematic parasitic in carp culture not only in government farm like Begnas and Mirmi, but also in commercial farms in most of the fishery areas of the country. Fin rot were more commonly reported during winter months affecting common carp, Silver carp, Bighead carp, Fingerling Fish causing fin erosion in them. Ascites in brood fishes (Trishuli) was noticed which may be due to bacterial infection and due to nutritional deficiency. Besides this, white spot in the gills (a protozoan parasitic disease) was perceived and to control it Neodox with Formalin (150ppm) was used and was found to be very effective. This study also identified some fish health management related problems in fish farms of Nepal such as lack of assistance, poor technical knowledge, and lack of suitable diagnostic laboratory and their proper use.

A survey on epizootic ulcerative syndrome (EUS) was carried in carp fish (cyprinids) reared in ponds during January 2016 to January 2017 at six locations of Chitwan, Nepal. Outbreaks of EUS were observed in 39.6% of the carp during winter. EUS infection was the most for Cirrhinus mrigala (47.3% of the 170 samples) and the least for Labeo rohita (12.3% of the 65 samples). EUS infected fish weighing range between 15g-300g were characterized as extensive deep ulceration on head, dorsal and lateral part of body and at caudal peduncle region. Histopathology examination of affected tissue of skin with adjacent muscles showed mycotic granulomas indicated a positive diagnosis for EUS. Survey results indicate that poor water quality in undrained ponds, uncontrolled entry of flooded water into the pond, runoff water from adjacent paddy field and use of contaminated equipment and seine nets were found to trigger risk for EUS infection in carp pond. Impact assessment of EUS showed that average economic loss due to EUS fish disease was 2257.92 kg/ha / year (33.01%) of the expected production. The highest economic loss of 1432.14 kg/ ha/year (53.53%) was estimated for large farm and lowest loss of 950 kg/ha/year (5%) for medium size farm. The simultaneous application of Ciphalexin in feed at 80mg.kg -1 biomass of fish for 15 consecutive days and two applications of Kohrsolin-TH at 900 ml/ha (1 m pond depth water) at weekly interval was found effective to control EUS infection in carps. The combined efficacy of these two drugs was estimated to be 97.7% control of EUS infection in carp fish.

Tail and fin rot is one of the most economically important disease throughout the world. Occurrence of tail and fin rot and emergence of antibiotic resistance in trout farming has mandated extensive survey, characterization of dominant causative agents followed by screening of effective antibiotics. In present study, predominant fin and tail rot causing bacterial pathogens were isolated from samples collected from fifteen rainbow trout farms of major trout pocket areas i.e. Rasuwa, Nuwakot, Dhadhing, Sindhupalchowk, Lalitpur and Kaski districts of Nepal. All the isolates were further tested for pathogenicity, which showed virulence in fancy carp (Cyprinus carpio haematopterus). Pseudomonas spp and vibrio spp showed more virulence. Antibiotic susceptibility test revealed that all the commonly used antibiotics (Amoxicillin, Azithromycin, Neomycin, Oxytetracycline and Streptomycin) were completely resistant. Among presently used antibiotics, Cephalexin was resistance in all the farms while Doxycycline was found completely resistant in two farms and Moxifloxacin was effective in general. Positive correlation between disease occurrence and water parameters were observed among various trout farms. Lack of knowledge regarding use of antibiotics, development of multidrug resistance bacteria and downstream effect of antibiotics used in trout farms was observed among farm's owner and farmers, implicating a need to develop an effective protocol in fresh water aquaculture in Nepal.

This study was conducted to assess the ichthyofaunal diversity of Bhagairia Lake located in Bardiya district, Nepal from August 2019 to February 2020. For this research monthly sampling was done to assess ichthyofaunal diversity and water quality parameters i.e. water temperature, water transparency, total dissolved solids, dissolved oxygen, pH, alkalinity, total hardness, ammonia, phosphate and nitrate from six sites around the lake.  A total number of 30 species of fish belonging to 8 orders, 13 families and 23 genera were recorded. Among these, Cypriniformes and Cyprinidae were the dominant order and family covering 50% and 44 % of fish species, respectively. Puntius sophore was found to be the dominant fish species with a catch composition of 12%. Maximum fish catch (214 individuals) was recorded in February whereas, minimum fish catch (140 individuals) was recorded in August. The fish catch was found to be positively correlated with dissolved oxygen (r= 0.912), pH (r= 0.876), alkalinity (r= 0.840) and total hardness (r= 0.876). Shannon diversity index was the highest in August (3.14) and lowest in November (2.87). Margalef's richness index was highest in the month of August (5.276) and lowest in February (3.727) whereas, Sheldon evenness index was highest in February (0.925) and lowest in September (0.823). This study revealed that Bhagairia Lake is rich in fish faunal diversity and consists of native, cultivable, ornamental and rare species of fish.

In this study, we describe a miniature sisorid catfish of the family Erethistidae, as a new distributional record of Pseudolaguvia nubila from the Baandhkhola (stream), a tributary of Narayani River inCentral Nepal. Pseudolaguvia nubila shows its distribution to Nepal is distinguished from its congeners by combination of characters, such as-two broad and distinct yellowish vertical bands at the origin of dorsal fin and anal fin, smooth outer edge of the dorsal fin spine, dorsal fin spine length 13.23-17.60 % SL, pectoral fin length 24.89-26.27 % SL, pectoral fin spine length 18.39-19.48 % SL and body depth at anus 17.22-18.69 % SL.