Diurnal Ammonia and Urea Excretion Rates in the Juvenile European Sea Bass, Dicentrarchus labrax Fed Diets Containing Cotton Seed and/or Canola Oils

This study investigated the effects of total fish oil replacement by cotton seed and/or canola oils on daily total ammonia and urea-nitrogen excretion rates in the juvenile European sea bass. Iso-nitrogenous and iso-energetic diets formulated to totally replace Fish Oil (FO100) by Cotton Seed Oil (CSO100), Canola Oil (CO100) and equal combination (CSO50/CO50) of these Vegetable Oils (VOs) were fed to fish to apparent satiation and daily fluctuation of Total Ammonia Nitrogen (TAN) and urea-N were measured after 24 h. There was a delay in times of the occurrence of peak excretions in fish fed diets containing VOs. Daily TAN excretion rates decreased whereas daily urea-N excretion increased with the inclusion of VOs in diets and this was particularly the case in fish fed dietary treatment CSO50/CO50 as daily urea-N excretion expressed as percentage of Consumed Nitrogen (CN) was significantly (p<0.05) higher than that of fish fed FO100 diet. There was no significant difference in the theoretically calculated Retained-N + Fecal-N values among the treatments. This study indicated that European sea bass utilized both VOs effectively as an energy source but altered dietary n-3/n-6 ratio seemed to play a part in the nitrogenous excretion mechanism in the European sea bass.