ISOLATION AND CHARACTERIZATION OF SELECTED GUT BACTERIAL FAUNA OF GOLDEN MAHSEER (TOR PUTITORA)

Abstract

Background: The golden mahseer (Tor putitora) is an endangered fish of the Himalayan rivers and the national fish of Pakistan. It is now bred in culture facilities so that young fish can be released back into rivers. Very little is known about the bacteria that live in its gut. Some of these bacteria are harmless in a healthy fish but cause disease when the fish is under stress, so it is useful to know which species are present and which antibiotics still work against them.

Methods: Nine apparently healthy golden mahseer samples were collected in Attock District, Punjab, between July and November 2025. Five were obtained from the Mahseer Fish Hatchery at Garyala and four were caught from tributaries of the River Indus. The gut of each fish was removed under sterile conditions and homogenized in normal saline. The homogenate was diluted to 10⁻⁵ and spread on MacConkey agar and blood agar, then incubated at 37 °C for 24 to 48 hours. Pure isolates were studied for colony appearance and Gram staining and were identified with the catalase test, oxidase test, sugar fermentation test, urease test, indole test and citrate test. Identifications were confirmed with the API 20E kit. An Antibiotic Sensitivity Test (AST) was carried out by the Kirby-Bauer disc diffusion method using six antibiotics.

Results: Seventeen isolates were obtained, eight from cultured fish and nine from wild fish. All were Gram negative rods. Three species were found: Aeromonas hydrophila (9 of 17, 52.9%), Klebsiella pneumoniae (7 of 17, 41.2%) and Pseudomonas sp. (1 of 17, 5.9%). In cultured fish A. hydrophila was the most common at 62.5%, followed by K. pneumoniae at 37.5%. In wild fish, A. hydrophila and K. pneumoniae were equally common at 44.44% each and Pseudomonas sp. made up the remaining 11.11%. The AST showed that all 17 isolates were resistant to erythromycin, penicillin and ampicillin. Three isolates (17.6%) were also resistant to doxycycline. All 17 were sensitive to ceftazidime and cefepime.

Conclusion: Healthy wild and cultured golden mahseer carry gut bacteria that can turn harmful under stress, and these bacteria are already resistant to several common antibiotics. Ceftazidime and cefepime still worked against every isolate. Regular bacterial checks, good water quality and careful use of antibiotics are needed in the culture facilities that breed this endangered fish.