Some experimental observations on gut passage time, egestion rate and faecal pellet production of brackish water mysid <i>Neomysis integer</i> (Mysidacea: Crustacea) feeding on different food items

Gut passage times in Neomysis integer were calculated by measuring voided faecal pellets when feeding ad libitum on a variety of environmentally relevant food types and a reference diet of Artemia salina nauplii. When feeding on A. salina nauplii, gut passage times were variable (from 4.1 to 12.9 h), but significantly longer than when feeding on the post-naupliar stages of the calanoid copepod Eurytemora affinis (2.6 h). Estuarine flocs passed through the intestine within 0.5 hour after ingestion, and N. integer produced daily up to twice its own body length in compact faecal material. The gut residence time of macrophytal detritus was 1.9 h and no difference was found between fresh and aged detritus.The egestion rate of Neomysis integer feeding on estuarine flocs (0.163 ± 0.001 mm3 h-1) was significantly higher than in all other treatments (0.011 ± 0.001 mm3 h-1). The faecal pellet production rate, when feeding on flocs, amounted to 0.044 mgDW mgDW-1 h-1. Preliminary results on the C:N ratio of food and faecal pellets demonstrated a general enrichment in nitrogen in the faecal pellets, probably due to bacterial growth on the pellets, the peritrophic membrane and disintegrating cells of the mysids intestine. The faecal pellets produced by Neomysis integer are still potential sources of energy themselves. Scanning electron micrographs of faecal pellets produced on the different food types give details about the peritrophic membrane and pellet content