Methods of measuring feed digestibility in the green abalone (Haliotis fulgens)

Various methods of calculating feed digestibility in the green abalone were compared. The total fecal collection technique was evaluated by comparing it with two different marker methods, one external (chromic oxide) and one internal (acid-insoluble ash). To obtain this information, a funnel-shaped digestibility chamber was designed. All the chambers (experimental units) were suspended in a square tank (200-1 capacity) containing aerated seawater and with airflow and temperature kept constant (0.5 l/min, 19 +/- 0.5 degreesC). Two abalone (2 years old; 4.8 +/- 0.69 cm; 14.1 +/- 6.04 g) were placed in each chamber. All animals were fed daily with a similar diet containing 1% chromic oxide. After 1 week of acclimatization to the chambers and the experimental diet, feces were collected for the next 45 days to ensure that there were sufficient samples to perform all the evaluations. The results showed that the digestibility coefficients obtained with total collection and with acid-insoluble ash marker were similar (80.5 +/- 2.73% vs. 84.4 +/- 5.21%, respectively), whereas using a chromic oxide marker produced a significantly lower value (61.7 +/- 2.0%). The advantages and disadvantages of each technique are discussed. We also suggest some modifications to enable the acid-insoluble ash method to be run using a smaller sample size (200 mg). (C) 2002 Elsevier Science B.V All rights reserved.