Introduction
Probiotics are “live microbial feed supplements which beneficially affects the host animal by improving its intestinal microbial balance”(Fuller, 1989) . Exposing fish larvae to selected probiotics has been proven to improve their health and increase their resilience to pathogens and disease due to the gastrointestinal microbiota dependency on the external environment (Gatesoupe, 1999). Probiotics also compete with pathogens
for nutrients and adhesion sites, which help to stimulate the immune system (Gatesoupe, 1999).
Materials and Methods
This trial tested the use of lactic acid bacteria (LAB) on pikeperch ( Sander lucioperca ) larvae during first feeding. The trial included the use of two probiotic treatments and one control (no probiotics). The first treatment exposed the live feed to LAB, while on the second treatment, LAB was used on the live feed as well as in larval tanks. Pancreatic (α-amylase, bile salt-activated lipase, total alkaline proteases) and gastric (pepsin) enzyme activities were determined as well as the microbiome from the larvae and the rearing water during. The trial duration was 18 days and samples of larvae and water were taken at 7, 14, 21 dph from each treatment.
Results
Significant differences were found between treatments in terms of enzyme activity at 7days post hatching (dph ) when looking at a lkaline protease, a mylase, l ipase and p epsin. Further significance was foun d on l ipase activity at 21 dph.
The use of LAB also had significant differences on the microbiome abundance and diversity on the larvae, as well as on the rearing water. Results showed a significant variation of the microbiome
with time, as well as a between treatments. Such effects might be the one of the main factors for the difference on survival between treatments.
Larvae exposed to LAB via the live-feed and the rearing water had a significant higher overall survival rate (88 %) than the other two treatments at 21 dph. At the same time, larvae exposed to the probiotic treatment had a significantly higher TL (7.34 and 11.82 mm) after 14- and 21-days post hatch (dph) compared to the control treatment (5.99 and 10.67 mm).
Conclusions
The results suggest that the use of LAB in both live feed and rearing water during pikeperch larval stage has a positive effect by enhancing early enzyme activity, controlling microbiome diversity and improving the growth and survival rates.
References
Fuller, R. Probiotics in man and animals. J. Appl. Bacteriol.
1989 , 66, 365–78.
Gatesoupe, F. The use of probiotics in aquaculture.
Aquaculture
1999 , 180, 147–165.