~ 235 ~ International Journal of Fisheries and Aquatic Studies 2021; 9(1): 235-239 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 (GIF) Impact Factor: 0.549 IJFAS 2021; 9(1): 235-239 © 2021 IJFAS www.fisheriesjournal.com Received: 25-11-2020 Accepted: 27-12-2020 Anifowose Olayinka Remilekun Department of Veterinary Medicine, Faculty of Veterinary Medicine, University of Ibadan, Nigeria Oladosu Gbolahanmi Akinola Department of Veterinary Medicine, Faculty of Veterinary Medicine, University of Ibadan, Nigeria Oladele Oludotun Olubusola Department of Veterinary Medicine, Surgery and Radiology, Faculty of Veterinary Medicine, University of Jos, Nigeria Corresponding Author: Anifowose Olayinka Remilekun Department of Veterinary Medicine, Faculty of Veterinary Medicine, University of Ibadan, Nigeria Causal factors of mass mortality of hatchery reared Clarias gariepinus fry during exogenous feeding Anifowose Olayinka Remilekun, Oladosu Gbolahanmi Akinola and Oladele Oludotun Olubusola DOI: https://doi.org/10.22271/fish.2021.v9.i1c.2409 Abstract The study investigated the causal factors associated with mass mortality of hatchery-reared Clarias gariepinus Burchell 1822 fry during exogenous feeding. A feeding trial and fry re-infection trial were conducted using four different starter diets. The food samples were fed to 480 post-yolk-absorbed fries for 21 days in two replicates. Samples of dead fry were cultured for bacteria using standard methods. The total aerobic and coliform were significantly higher in all food samples, meanwhile, alkaline pH (9.25±0.34) and low dissolved oxygen (4.5±1.08) were not significantly different (P>0.05) in all water tanks. The bacterial pathogens isolated from dead fries were Aeromonas hydrophila Stainer, 1943 and Pseudomonas aeruginosa Migula, 1990, whereas significantly higher mortality in experimentally infected fry was observed (α < 0.05). Mass mortality of C.gariepinus fry observed in this study was associated with bacterial pathogens, bacterial contamination of food, alkaline pH, and low dissolved oxygen. Keywords: fry, mortality, food samples, Clarias gariepinus, pH 1. Introduction Aquaculture, which is dominated by African catfish farming, has in recent decades increased at a phenomenal rate in many parts of the country, including Southwest Nigeria [19] . Fertilization, hatching, and early survival of larvae are vital for successful aquaculture of the African catfishes and this has been investigated earlier [5] . It has been estimated that 10% of all cultured aquatic animals are lost as a result of infectious disease [18] , meanwhile, environmental circumstances such as poor water quality, fluctuations in temperature, poor nutrition, overcrowding, poor handling, and transportation are common in intensive fish farming could pose stressful conditions to fish and make them more susceptible to a wide variety of pathogens. Hatchery propagation of fish seeds is sometimes hampered by mass mortality during fry nursing, with environmental factors, first feed sources, and infectious agents exerting great influence in this regard [9] . Mass mortality of fry would result in poor fingerling harvest and hence inadequate supply of fish seed which will, in turn, result in inadequate fish production. The suitability of first feed sources for fry rearing is very important in the light of the need for good growth and high survival rates [3] and the high cost of importing encapsulated artemia has necessitated the search for other first feed sources with fish culturists using several materials to rear the larvae of Clarias gariepinus [2] . The studies on the causal factors of Clarias gariepinus fry mortality following exogenous feeding in Nigeria have not been reported. Therefore, this study sets out to investigate the causal factors of mass mortality of hatchery-reared C.gariepinus fry during exogenous feeding. 2. Materials and Methods 2.1 Handling of experimental Fish Ethical clearance and valid approval were obtained from the University of Ibadan, Ethical Committee for Medical and Scientific Research before the commencement of the experiment. Fry used in this study were handled according to the Canadian Council on Animal Care’s Guide to the Care and Use of Experimental Animals [10] .