Probiotic and formaldehyde treatments of Artemia nauplii as food for larval pollack, Pollachius pollachius

Abstract

Formaldehyde was used to disinfect Artemia cysts and nauplii, while introducing two probiotics in the enrichment process: Bactocell ( Pediococcus acidilactici) and Levucell ( Saccharomyces cerevisiae). The disinfectant was selected due to its potential compatibility with probiotics, since it was more effective against Gram-negative bacteria than against lactic acid bacteria and yeast. However, the presence of formaldehyde reduced the intake of P. acidilactici in Artemia. Consequently, the disinfection was stopped before Bactocell supplementation to the nauplii fed to pollack ( Pollachius pollachius) larvae. The mean weight of pollack was higher with this probiotic treatment. Growth was even better with the combination of Levucell and Bactocell, but the yeast should be introduced circumspectly. A high bacterial load was found in the nauplii enriched with Levucell, but not treated with formaldehyde. In the absence of Bactocell, the discontinuation of disinfecting Artemia after Levucell enrichment caused poor growth of pollack. Resistant strains had emerged after 3 months of daily cyst incubation with 50 mg l −1 formaldehyde, rising from 1.4 CFU per newly hatched nauplius before the experiments, up to 3.4×10 4 CFU nauplius −1 by the end of 3 months. The phenotypes and genotypes of these opportunistic resistant strains were quite different from the initial resistant strains. Particular attention was paid to Vibrio alginolyticus-like isolates that were not detected before the experiments. These isolates were compared by amplified ribosomal DNA-restriction analysis (ARDRA) and RAPD to two reference strains previously isolated in turbot larvae, indicating some genotypic distance between the new isolates and the reference strains. Thus, the formaldehyde treatment cannot be recommended due to the risk of resistance spread. It was concluded that P. acidilactici is a promising probiotic for fish larvae. Its combination with S. cerevisiae may be valuable, but on the condition that a concentrated form that would not jeopardize the bacterial balance in the absence of disinfectant should be prepared.