Rapid screening of potential probionts from the gut microbiota of climbing perch, Anabas testudineus

The intestinal microbial community has crucial functions for their vertebrate host. Several studies in fish showed that their gastro-intestinal tract harbors a diverse population of bacteria that supplies exogenous nutrients, enzymes, fatty acids and vitamins to their host. Most studies on probiotics involved their practical use for aquaculture, but are limited for the ornamental fish industry. Hence, this study aimed to screen the gut microbiota of a freshwater fish, Anabas testudineus, for potential probiotic candidates for the ornamental fish industry. Gut bacteria were obtained from the gut of climbing perch by plating of serially-diluted samples of the gut contents onto Nutrient Agar (NA). In vitro antagonistic activities of these gut bacteria against a fish bacterial pathogen, Aeromonas hydrophila, were determined by spot-on-lawn method. Isolates that had strong antagonistic activities against A. hydrophila were further characterized using standard staining and biochemical techniques. Rapid screening of the gut microbiota of climbing perch resulted in the identification of a promising probiont, Kurthia gibsonii through sequencing of its 16S rRNA gene. This bacterium is a member of the Planococcaceae family and is a Gram-positive, non-spore forming and rod-like bacterium. The isolate is yellowish in appearance and has a filamentous colony on nutrient agar. It exhibited catalase and amylase activities. Immersion challenge of freshwater ornamental fish with the bacterial isolate showed no mortality at 15 days after exposure. Taken together, the present study demonstrated that the gut microbiota of fish is a rich source of probiotic candidates that can be utilized during the culture of freshwater ornamental fish.This work is partly supported by the University of San Agustin Professorial Chair Research Grant titled, “Gut Microbiome: A Potential Source of Probiotic Candidates for Ornamental Fish” awarded to CMA Caipang. The authors of this paper would like to thank the support provided by their respective institutions; namely, the University of San Agustin and SEAFDEC Aquaculture Department during the preparation of the manuscript

Utilization of sodium bicarbonate as anesthetic during routine husbandry activities in ornamental fish

The tropical ornamental fish industry requires the stock to be reared in captivity before being sold; thus, exposing them to various handling- and transport-related stressors. A number of commercially available anesthetics are used during fish husbandry procedures, but these products are expensive and not readily available to small-scale ornamental fish operators. The use of sodium bicarbonate as an inexpensive anesthetic during routine husbandry activities in molly, Poecilia sp., a freshwater ornamental fish was assessed in terms of its effect on sedation, recovery and survival post-exposure in three independent experimental runs. Juvenile molly were exposed to sodium bicarbonate at a concentration of 100 g L−1 and the time to sedation and recovery were monitored. It took longer for the fish to be fully sedated than their recovery. Survival of the fish a week post-exposure ranged 40-60%. Simulated transport of fish for 6 hrs in water containing 1 g L−1 of sodium bicarbonate showed survival ranging 70-100% a week after transport. These findings demonstrated that sodium bicarbonate could be potentially used as a low-cost anesthetic during handling and short-term transport of ornamental fish. Future studies shall focus on discovering the underlying physiological mechanisms in fish following sedation with this chemical