Tg. Gaylord et Dm. Gatlin, Dietary lipid level but not L-carnitine affects growth performance of hybrid striped bass (Morone chrysops female X M-saxatilis male), AQUACULTURE, 190(3-4), 2000, pp. 237-246
The objectives of this experiment were to determine if dietary lipid levels
in excess of previously reported minima would increase performance of hybr
id striped bass, and to determine if supplementation of L-carnitine would i
mprove growth and/or body composition when feeding elevated dietary lipid.
Therefore, a 2 X 4 factorial design was utilized to test the efficacy of di
etary L-carnitine at 0 and 3000 mg/kg diet at each of four lipid levels (5%
, 10%, 15% and 20%). Semipurified diets were formulated to contain 40% crud
e protein and dextrin was substituted for menhaden oil at a rate of 2.25 to
1 to maintain digestible energy at approximately 14.2 kJ/g. Juvenile recip
rocal cross hybrid striped bass initially averaging 2.5 g/fish were culture
d in a 5 parts per thousand brackish water recirculating system and fed twi
ce daily at a rate approaching apparent satiation.
At the end of the 8-week feeding trial, L-carnitine supplementation did not
influence weight gain, but dietary lipid level did, with the lowest value
(1084% of initial weight) achieved by fish fed 5% lipid and the highest (13
43%) by fish fed 15% lipid; fish fed 20% lipid had intermediate weight gain
(1215%). Feed efficiency also was influenced by dietary lipid with fish fe
d the 10% and 20% lipid diets having higher feed efficiency values than tho
se fed the 5% and 15% lipid diets. Body condition indices were only slightl
y altered by L-carnitine supplementation, but dietary lipid over 10% influe
nced body condition. Liver composition was altered by dietary lipid level b
ut not L-carnitine supplementation. As dietary lipid level increased, liver
lipid increased and liver glycogen decreased dramatically, especially in f
ish fed the diet with 20% lipid, which had no soluble carbohydrates. Muscle
composition was unaltered by any dietary treatment. In conclusion, hybrid
striped bass generally did not utilize dextrin as efficiently as lipid, and
lipid levels between 10% and 15% of diet provided maximum growth with inte
rmediate lipid deposition. (C) 2000 Elsevier Science B.V. All rights reserv
ed.