Evaluation of acid-insoluble ash as an indicator for digestibility determination with red drum, Sciaenops ocellatus, and hybrid striped bass, Morone chrysops x M. saxatilis.

摘要

This study was conducted to determine the suitability of acid-insoluble ash (AIA) as an indicator of digestibility in red drum and hybrid striped bass. Two experimental diets were used for the red drum trials. These diets used menhaden fish meal as the sole protein source and were formulated to contain 40% crude protein and 8.2% lipids with an estimated digestible energy value of 3.5 kcal/g. Either chromic oxide or Celite was included in the diet at one percent of dry weight to serve as the inert marker. The diets used for the hybrid striped bass trial were based on an experimental feed mix formulated to contain 53% crude protein and 15% lipid with an estimated digestible energy value of 4.0 kcal/g. The 3 experimental diets for hybrid striped bass were prepared from the basal mixture and supplemented with either 1 or 1.5% Celite or 1% Celite plus 0.5% chromic oxide. In the first trial, the apparent digestibility coefficients (ADCs) calculated based on chromic oxide provided a reasonable estimation of organic matter and crude protein digestibility (~62.2 and 75.6%). However, ADCs calculated based on either internal AIA in the chromic oxide diet or total AIA in the Celite diet failed to provide a proper estimate nutrient digestibility. The AIA content in the faecal samples from red drum fed either chromic oxide or Celite diets 4 h post-feeding was similar or even lower than the dietary concentration in contrast to the increased concentrations of chromic oxide in the faecal samples. In the 2nd trial, faecal samples were collected one hour later than the first trial. The ADCs for organic matter and crude protein calculated based on AIA were lower than those calculated based on chromic oxide. Aggressive feeding was observed with hybrid striped bass throughout the trial. ADCs calculated based on chromic oxide and AIA for fish fed the one percent Celite and the one percent Celite plus 0.5% chromic oxide diets were insignificantly different. ADCs calculated based on AIA for fish fed the 1.5% Celite diet were significantly lower than the other 2 diets, indicating that high AIA inclusion affected the digestibility estimation for hybrid striped bass.