Feed transit and apparent protein, phosphorus and energy digestibility of practical feed ingredients by Senegalese sole (Solea senegalensis)

A study was conducted with Senegalese sole (Solea senegalensis) to determine the apparent digestibility coefficients (ADCs) of protein, phosphorus and energy in practical feed ingredients. The digestible energy (DE) content was also evaluated. Test ingredients were anchovy fishmeal, solvent-extracted soybean meal, corn gluten and wheat meal. Due to their low cohesion, sole faeces were collected directly in posterior intestine by dissection. The feed transit time along the gastrointestinal tract was assessed in Senegalese sole (body weight: 140 g) reared at 19 °C by means of a radiographic technique, following a single meal of a radio contrast agent, barium sulfate. Feed digesta accumulated in the posterior intestine 10-12 hours after the single meal and its total egestion was achieved at 24 hours following the meal. Dry matter digestibility of the various test ingredients was high (ranging from 88 to 93%), with lowest values being found for soybean meal and corn-gluten. Protein digestibility was high (above 91%) for fishmeal and corn gluten, intermediate for soybean meal (87%) and moderate for wheat meal (59%). Energy digestibility varied between 88 and 93% for soybean meal, corn gluten and anchovy fishmeal and was reduced in wheat meal (73%). The DE (MJ/kg) content varied from 16.2 for anchovy fishmeal, 15.1 for corn gluten, 13.5 for solvent-extracted soybean meal and 10.1 for wheat meal. Phosphorus digestibility was highest in fishmeal (58%) and greatly reduced in vegetable ingredients (28 to 33%). In general, our data shows that flatfish species, Senegalese sole, despite its high dietary protein requirement, digests vegetable ingredients relatively well, opening the opportunity for the development of practical feeds with high levels of plant-protein sources.