Potential use of radiography for measuring feed intake of southern rock lobster (Jasus edwardsii)

The potential of using radiography for measuring feed intake in southern rock lobster Jasus edwardsii (Hutton) was evaluated. Lobsters (14-40 g) readily consumed feeds containing radio-opaque marker (400-450 μm). Marker particles were clearly identified in the stomach 90 min after feeding enabling feed intake to be estimated. Initially low estimates (15 ± 17%; mean ± S.D.) of feed intake (expressed as percentage of gravimetric estimates) were recorded due to loss of markers prior to ingestion. Radiographic estimates improved (100 ± 23%; mean ± S.D.) when changes to pellet diameter (1.5 mm), moisture content (11%) and binding agent (alginate) were made. Thus, estimates were dependent on pellet diameter and resistance to fragmentation prior to ingestion. To test for the presence of feeding hierarchies in groups of lobsters an experiment was conducted to examine the effect of ration level (high ration: 2.0% BW day-1 and low ration: 0.2% BW day-1) on intra-individual (measured as coefficient of variation for feed intake: CVc) and inter-individual variation (measured as mean share of the group meal: MSM%). There was a significant (P<0.05) negative correlation between CVc and MSM% for the low ration treatments which indicated that small lobsters (CVc=114 ± 19% and MSM%=22 ± 10%: mean ± S.D.) were less successful than large lobsters (CVc 44 ± 11% and MSM%=41 ± 13%: mean ± S.D.) at obtaining feed. This may be indicative of the formation of feeding hierarchies. © 2002 Elsevier Science B.V. All rights reserved.