The effect of varying levels of fiber, protein, and lipid feed component levels on gut passage time (GPT) and gut passage rate (GPR) of Farfantepenaeus aztecus (Pérez Farfante & Kensley 1997), Litopenaeus setiferus (Pérez Farfante & Kensley 1997), and Litopenaeus vannamei (Pérez Farfante & Kensley 1997), was examined in field feeding trials in a tidal creek and shrimp culture pond. Feeding trials were conducted in flow-through enclosures and feeds were thoroughly mixed with inert fluorescent latex beads to facilitate observation of the feed location within the guts of the shrimp. Rather than being able to continuously view feed passage through the shrimp guts (as is possible in the laboratory), we developed indirect methods that allowed us to obtain periodic “snapshots” of feed movement through shrimp guts at 10-min intervals, which were then used to calculate GPT and GPR. We expected to observe differences in GPTs because invertebrates are known to adjust their gut passage dynamics and GPTs should change as a function of food quality. Surprisingly, very large variations in feed component levels, whether fiber, protein, or lipid, did not cause any large differences is GPT within any of the three species. Mean GPTs ranged from 65.7–90.5 min in F. aztecus and L. setiferus and from 48.3–66.6 min in L. vannamei. GPRs were not constant, ranging from 5–16 mm/min when GPTs were short and from 0.1–2 mm/min for longer GPTs. Finding little change in GPTs with large changes in food quality was consistent with previous studies using other methods.
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Vol. 24 • No. 1