Response of common carp (Cyprinus carpio L.) to supplemental DL-methionine and different feeding strategies

The common carp (Cyprinus carpio) is an agastric fish, meaning absorption of nutrients is highly dependent on the rate of feed passage in the gut. Two diets and 3 feeding strategies were used in a 2 × 3 factorial experiment, conducted to determine whether utilization of supplemental DL-methionine (DL‐Met) interacts with feeding strategies. Diets 1 and 2 contained, respectively, no Met supplementation (Met deficient diet with Met level of 0.45% Met in DM) and supplemented with DL-Met (Met balanced diet with Met level of 0.86% Met in DM). The three feeding strategies included, hand feeding twice daily to apparent satiation (feeding strategy 1), pair feeding the same amount of feed as in strategy 1 continuously by means of an automatic feeder over 2 × 6 h periods (feeding strategy 2), and continuously feeding a fixed rate of 1.4% BW using an automatic feeder (feeding strategy 3). The fish, with a mean initial weight of 239 g, were fed for 82 days in a recirculation system. The results indicated that supplementation of DL-Met in the diet improved (P < 0.05) final weight(483 vs. 424 g), daily weight gain, feed consumption, feed efficiency (1.60 vs. 1.92 g DM weight gain− 1) and protein digestibility (90.7 vs. 87.9%). Supplemented DL-Met also resulted in increased carcass protein and reduced carcass fat. Plasma levels of methionine and arginine were higher with supplemented dietary DL-Met, while plasma levels of lysine and serine were lower (P < 0.05). Feeding strategy also affected performance and except for feed efficiency no interactions with dietary methionine supply were detected. Compared to feeding strategy 1 feeding strategies 2 and 3 improved (P < 0.05) protein digestibility, whereas only feeding strategy 3 increased organic matter digestibility. Continuous feeding (strategies 2 and 3) increased (P < 0.05) final weight, daily weight gain and improved feed efficiency. The positive impact of continuous feeding (strategies 2 and 3) compared to twice daily feeding was more pronounced with Diet 1 indicating that also at low feeding frequency supplemental DL-Met is effectively utilized for growth. Feeding strategy 3 was accompanied with a lower feed consumption in comparison to feeding strategies 1 and 2. Feeding strategy did not influence the chemical composition of the carp. The study established that DL-Met can be an effective nutrient for carp, that feeding frequency impacts nutrient utilization and that this effect is not restricted to DL-Met supplemented diets.

► Crystalline DL-Met affects growth, feed intake and feed conversion of carp.
► Digestibility, carcass composition and AA content of blood were influenced.
► The effect of crystalline DL-Met was mainly independent of feeding strategy.
► Feeding was 2 × hand feeding, pair feeding and a fixed rate continuously.
► Feeding strategy affects performance parameters of carp.