Survival, growth and feeding rate of the mysid <i>Neomysis integer</i> (Crustacea: Mysidacea) on laboratory-made estuarine aggregates

Laboratory-generated aggregates (flocs) made from natural estuarine water of the oligohaline part of the Schelde estuary (Belgium) were administered to the brackish water mysid Neomysis integer in order to determine their value as a dietary item. Survival, growth, intermoult period, growth factor and intermoult growth rate of subadult mysids (4 - 10 mm standard length) were monitored over 4.5 weeks in a roller table. In a first experiment, the effect of tidal dynamics on the floc formation process, as well as on the floc size and shape was followed. Also, we evaluated the effect of continuous rotation in the roller tanks on the growth of N. integer to be negligible. Subsequently, we performed a growth experiment with N. integer reared on the laboratory-made aggregates and estimated the feeding rate. The estuarine aggregates are a valuable food source for the mysids as they showed good survival (80 %) and grew substantially on this dietary item (0.08 ± 0.01 mm d-1), although growth is slower than on Artemia nauplii (0.11 ± 0.01 mm d-1). The high feeding rate of subadult Neomysis integer on the laboratory-made flocs (38 flocs ind-1), may compensate for their low energetic value. The roller table is an adequate tool for feeding experiments with N. integer on the fragile estuarine aggregates. For Neomysis integer living in the maximum turbidity zone of estuaries, the estuarine flocs may be an important additional food source, especially in periods when mesozooplankton prey (mainly calanoid copepods) is scarce. The rich bacterial and protozoan communities associated to the flocs as well as the incorporated amorphous organic matter, normally too small to be efficiently consumed by mysids, become part of their diet. This pathway thus constitutes a short-cut in the estuarine food chain