Weaning of Burbot, Lota lota (L.) from Live to Dry Feed Using NaCl as Dietary Attractant

Abstract

Weaning of 150 days post hatch Lota lota from live feed (zooplankton) to formulated dry feed (FDF) was investigated. L. lota could not be forced from live feed to FDF. They refused FDF for periods up to 21 d. Body mass decreased for 20%, condition factor for 15%, and hepatosomatic index for 50%. In 21 days lasting co-feeding experiments with FDF and live feed L. lota selected exclusively the live feed organisms. NaCl in a concentration of 5% was a dietary feeding attractant for L. lota. When FDF was supplemented with 5% NaCl, L. lota could be abruptly weaned from live to dry feed. During a 21 d lasting experiment body mass increased for circa 40%, total length for 10%, condition factor for 5% and hepatosomatic index remained constant. These values were similar to live zooplankton feeding. However, increased mortality of > 20% was recorded for fish fed with the 5% NaCl containing FDF. To reduce mortality FDF was supplemented with zooplankton meal to upgrade its quality and extruded to optimize its density and sedimentation rate. With the adjusted FDF mortality rates were reduced to < 5%. Using the optimized dry feed easy and sustainable weaning protocols were developed where NaCl and zooplankton meal were gradually reduced to adapt fish to pure FDF.