Abstract
BackgroundThe ubiquitous and opportunistic bacterial pathogen Aeromonas hydrophila has been associated with ulcerative dermatitis in fish, especially under stressful conditions. It can cause severe losses in fresh water aquaculture and is particularly prevalent in tropical and subtropical regions. Fresh leaves from maize and bananas have been used as feed supplement by fish farmers in Vietnam and it has been reported that they may have phyto-prophylactic benefits. In the present study, a feeding trial was conducted to investigate the benefits of providing maize and banana leaves as feed supplement: to determine if they were taken up and digested by grass carp (Ctenopharyngodon idella), if this uptake resulted in improved growth performance, and if leaf supplementation protected fish when challenged with A. hydrophila by intramuscular injection.ResultsAll fish were fed an identical ratio of commercial pelleted feed relative to biomass. However, in 12/18 tanks, this diet was supplemented with either fresh banana leaves or fresh maize leaves; offered ad libitum. Addition of leaves increased the overall feed conversion ratio (FCR) significantly. However, if only the pellet were taken into account, then no difference was found between treatments. Changes to the isotopic composition of the fish showed leaf nutrient uptake occurred. No prophylactic effects of feeding banana or maize leaves were detected against infection with A. hydrophila, and the diet did not induce changes in the fish haematocrit. However, addition of the maize leaves was associated with significantly reduced severity of the skin lesions, which could improve the market value of the fish.ConclusionsAddition of the leaf supplement did not result in significantly improved growth performance. Similarly, the effect of the supplement on the fish survival to infection was not significant.
Highlights
The ubiquitous and opportunistic bacterial pathogen Aeromonas hydrophila has been associated with ulcerative dermatitis in fish, especially under stressful conditions
The feed materials used in this experiment differed in their chemical composition (Table 1): Maize leaves had a higher crude protein (CP) content than banana leaves: 27.9 and 20.0% of the total dry matter (DM) content, respectively, while the crude lipid (CL) contents were comparable between the two leaves (5.4% in the banana leaves and 4.9% in the maize leaves; Table 1)
The supplemental feeding of fresh maize and banana leaves did not significantly increase the growth performance of grass carp, which attests to the poor nutritional value of these types of plant materials
Summary
The ubiquitous and opportunistic bacterial pathogen Aeromonas hydrophila has been associated with ulcerative dermatitis in fish, especially under stressful conditions It can cause severe losses in fresh water aquaculture and is prevalent in tropical and subtropical regions. It is often stocked as the main species in semiintensive polyculture systems with other fishes [1] This practice enables small-scale farmers to produce fish for food security and sale at local markets, when using leaves from other farming activities as low-cost feed [1]. The most common treatments against bacterial diseases remain chemotherapeutic and antibiotic agents which, when applied indiscriminately, have been linked to the development of drug resistant bacteria [4, 5] These treatments are often not available or affordable for small-scale farmers in rural areas like in Northern Vietnam. In Clarias gariepinus larvae, banana leaves have been reported to reduce mortalities and improve growth and weight gain parameters [12]
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