Can Peak Buccal Cavity Pressure Be Used to Predict Peak Fluid Speed during Suction Feeding in Fishes?

HEYLAND, A., MOROZ, L.L.; [email protected]. The Whitney Laboratory for Marine Bioscience, Saint Augustine, University of Florida SEARCH FOR NEURONAL TRANSCRIPTS INVOLVED IN THE METAMORPHIC TRANSITION OF THE SEA HARE APLYSIA CALIFORNICA Metamorphosis among many marine invertebrate species involves a radical transition from a larval to a juvenile/adult body plan that can occur in a remarkably short period of time. Metamorphic competence directly precedes this radical change in morphology and can best be described as the developmental potential of a larva to undergo the radical transition in response to environmental signals. Such signals (i.e. settlement cues, substrate architecture, temperature, food etc.) are modulated via neuronal gene networks. A metamorphic pattern with competence and a fast radical transformation evolved many times independently in animals and we hypothesize that similar signaling modules have been co-opted for the regulation of a) the development to competence and b) the interpretation and modulation of environmental signals. However the actual signaling architecture underlying these processes is largely unknown for the majority of marine invertebrate species. We used representative oligo-arrays constructed from transcripts obtained from the Aplysia californica (sea hare, Mollusca) central nervous system to explore the following two questions: 1) What neuron specific genes are expressed during development to metamorphic competence? 2) What neuron specific genes are expressed immediately after settlement, i.e. upon exposure to specific environmental signals. We validated our expression analysis of specific neuropeptides, nuclear hormone receptors and chemoreceptor molecules using in situ hybridizations. Support Contributed By: NIH, NSF, & McKnight BR Foundation. 44.6 HIGHAM, T.E., DAY, S.W., WAINWRIGHT, P.C.; [email protected]. University of California, Davis, Rochester Institute of Technology CAN PEAK BUCCAL CAVITY PRESSURE BE USED TO PREDICT PEAK FLUID SPEED DURING SUCTION FEEDING IN FISHES? Suction-feeding fish capture prey by rapidly expanding their buccal cavity, which generates a flow of water directed towards their mouth. A subambient pressure inside the buccal cavity is associated with this expansion, and the magnitude of this pressure differs considerably among species of fish and within an individual. Although peak sub-ambient pressure is thought to be proportional to fluid speed squared by Bernoullis principle, no study has measured both pressure and fluid speed simultaneously. Thus, we quantified buccal pressure and fluid speed simultaneously during feeding in four individuals of largemouth bass, Micropterus salmoides. We measured pressure by inserting a transducer through the skull of the fish so that the tip of the transducer was flush with the dorsal surface of the buccal cavity. We measured fluid speed using digital particle image velocimetry (DPIV). A laser sheet was positioned on the mid-sagittal plane of the fish so that the fluid speed could be measured along a transect extending from the center of the fishs mouth. We found that peak pressure was significantly correlated with the peak fluid speed (r2=0.61; P<0.01) of the same feeding. However, the magnitudes of the pressures were much greater (up to 5 times) than those estimated from the measured fluid speeds. We found that peak pressure preceded peak gape and peak fluid speed by an average of 14 ms and 18 ms, respectively. Thus, although correlated, pressure is sub-maximal at the time of peak fluid speed. In conclusion, a substantial amount of variation in peak fluid speed cannot be explained by peak pressure, suggesting that a mechanism other than pressure is being modulated by the fish in order to alter fluid speed. Supported by NSF IOB-0444554.