Wheatgerm flour in diets for Manila clam, Ruditapes philippinarum, spat

Abstract

Various diets for the spat of Ruditapes philippinarum were assessed, consisting wholly or partially of wheatgerm flour—diet A1: 100% of the daily food ration (4 mg AFDW (100 mg LW)−1) consisted of the microalga Isochrysis galbana, clone T-ISO; diet M2: 50% of the daily ration consisted of microalgae and the other 50% of flour; diet M3: 25% microalgae and 75% flour; and diet G: 100% flour. Two control diets consisting solely of microalgae were also assayed: diets A2 and A3, consisting of 50% and 25% of the daily ration, respectively. The composition of the wheatgerm used was: 18.2% of the total organic matter consisted of protein, 71.2% of carbohydrate and 10.6% of lipids, while the microalgae consisted of 27.8% protein, 38.3% carbohydrates and 33.8% lipids. The diets prepared with these two components are characterised by an increase in their carbohydrate content and a decrease in their protein and lipid content as the proportion of wheatgerm increases.

The highest growth rates were obtained for the spat fed diets A1 (final dry weight, 7.12±1.15 mg individual−1) and M2 (6.72±0.30 mg individual−1),with no significant difference being observed between the two diets. The spat fed diet M3 reached a final dry weight of 4.12±0.49 mg individual−1, a figure which is greater than that obtained with the control diets A3 (1.44±0.13 mg individual−1) and A2 (2.98±0.76 mg individual−1). The growth of the spat fed exclusively wheatgerm, diet G (1.55±0.08 mg individual−1), was similar to that obtained with control diet A3. The proportion of organic matter in the spat at the end of the experimental period is related to the nutritional value of the diet, so that the spat fed the diets with the greatest nutritional value (the highest growth rates) showed higher proportions of organic matter.