Gastrointestinal evacuation time, but not nutrient digestibility, of greenlip abalone, Haliotis laevigata Donovan, is affected by water temperature and age

The effects of water temperature (14, 18, 22 and 26 °C) and age (2-y-old, 6.7 g; 3-y-old, 25.7 g) on the gastrointestinal evacuation (GIE) time and apparent nutrient digestibility coefficients (ADC) for greenlip abalone (Haliotis laevigata). GIE time of greenlip abalone was evaluated using a marker diet containing chromic oxide and the total faecal collection technique. Additionally, GIE values were compared from samples collected from abalone that were sampled once only or repeatedly to compare the rigour of each method. GIE time was also assessed using radiography. GIE times were significantly affected by water temperature (P < 0.001) and age (P < 0.05). GIE times decreased for both age classes with increasing temperatures, and the GIE time of 2-y-olds was significantly faster than for 3-y-olds. GIE times never exceeded 60 h. There was no significant effect of either factor on the duration that the marker diet was voided, suggesting that differences in GIE times are due to factors other than the transit of feed through the intestine. Dry matter ADCs were not affected by temperature (P > 0.05) but were affected by age (P < 0.001; 2-y-old < 3-y-old). Protein and energy ADCs were not affected by temperature or age. Results may be used to predict purging times and also indicate that further investigations into feeding frequencies are recommended.