Identification and assessment of potential probiotics for the use in rotifers (Brachionus plicatilis) and Artemia used as feed for marine fish larvae

Chelsea Woods Nielsen

Probiotics are microorganisms which have beneficial effects on the host, including increased host response to pathogens and prevention of disease. Marine larval fish are susceptible to bacterial and viral infections during early development as they hatch underdeveloped with an immunologically naïve immune system. The use of live feeds in marine larval rearing transfers potentially harmful bacteria into the larval rearing tank. Live feeds, such as rotifers and Artemia, are non-selective filter feeders therefore enriching live feeds with probiotics is a way to both remove unwanted, and introduce beneficial, bacteria to newly hatched larvae. A screening process was used to select potential probiotics from the genera Shewanella, Vibrio and Pseudoalteromonas. Culture dependant techniques identified an isolate from each genera that demonstrated the highest inhibition properties against common marine fish pathogens. MALDI-TOF mass spectrometry and Sanger sequencing were used to determine the identity of these three isolates, the Vibrio isolate was successfully identified as V. scophthalmi, however the species of the Shewanella and Pseudoalteromonas isolates remain unresolved. Due to the nature of their culture, rotifers have an inherently high bacterial load which can be easily transferred to the fish larvae to which they are fed. Minimising these potentially harmful bacteria allows for beneficial probiotic bacteria to proliferate in the rotifer culture. However, disinfection techniques commonly used in fish hatcheries are often ineffective at low doses or lethal to the rotifer at higher doses. A minimum inhibitory concentration assay for antimicrobial peptides was performed against bacterial species common in rotifer cultures, however the peptides were ineffective under normal rotifer culture conditions (salinity at 25‰). Disinfection techniques can be used more favourably in Artemia enrichment. This study found, a short-term probiotic enrichment method resulted in a high probiotic retention in the Artemia at commercially relevant densities (500 – 5000 Artemia/ mL). Probiotic retention was improved when Artemia were disinfected with sodium hypochlorite after the fatty acid enrichment, whilst also reducing the unwanted bacteria species common to Artemia cultures. The use of a probiotic selection process identified candidate probiotics to be administered into the most common live feeds used in marine larviculture, rotifers and Artemia. Importantly, this study found the successful enrichment of probiotics in Artemia at high retention yields which may have significant positive impacts to the performance of marine finfish larvae.

Identification and assessment of potential probiotics for the use in rotifers (Brachionus plicatilis) and Artemia used as feed for marine fish larvae

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