Growth and nutrient utilisation of blackspot seabream (Pagellus bogaraveo) under different feeding regimes

The growth and nutrient utilization of blackspot seabream was studied under self-feeding or hand feeding for 90 days. Groups of 31 fish with an initial body weight of 24 g were fed either by hand two times a day (09:00, and 18:00 h) to apparent satiety or by self-feeders. The 90 days of the feeding trial included two periods: an adaptation period (30 days) required to achieve a constant number of feed demands per day and a subsequent experimental period (60 days). Final body weight and daily growth index were unaffected by the feeding regimes. However, the marked reduction in voluntary feed intake associated with similar nutrient gain on the self-fed group resulted in improved nutrient efficiency and in subsequent increased protein, lipid and energy retentions compared to fish hand-fed at set hours. The self-fed group displayed depressed malic (<62%) and fatty acid synthetase (<35%) activities as well as reduced triacylglycerol plasma levels, which correlated positively with feed intake and, at some extent, with fish lipid content. These results indicate the ability of blackspot seabream to adjust their lipid metabolism according to fish feeding rhythm. No effect of feeding method was however observed on glycolytic hepatic activities or on glucose, cholesterol and insulin plasma levels. Self-feeders led to similar growth (DGI, 1.4-1.5) but better efficiency (FCR, 1.0 vs. 1.5), and hence, can be regarded as a helpful tool to optimize feed distribution according to this species natural rhythm. The maximal number of demands occurring between 20:00 and 21:00 h (dusk/sunset), together with the fact that 61% of the feed demands took place during the night, reveals a preferential crepuscular/nocturnal feeding pattern of this species.