Feeding is how fish acquire energy for growth and reproduction1. Therefore, feeding behavior has been studied extensively. Fish feeding behavior depends on various factors such as flow, prey density, prey size, light, and predators2-11.
Among these factors,
However, these studies have focused on swimming fish in coral reefs or rivers, taking advantage of coral shelter that decreases the flow speed experienced by fish by more than 60%13-15. Garden eels, however, live in fringe areas of coral reefs and don't have shelter other than their burrow, which is why they are expected to have a unique feeding behavior depending on the flow.
Based on the above motivation, we are studying effects of flow speed on the garden eel's feeding behavior. The relationships between flows and the feeding behavior of garden eels (Gorgasia sillneri) was studied for the first time by Khrizman et al (2018) in the Red Sea16. In their research, they found that the eels maintained their feeding rate even under strong flow speeds by decreasing the drag force through bending their posture.
However, because the research was done in the field, it was hard to exclude effects of other environmental factors. For this reason, additional research in the controlled lab condition is needed.
The tank in the picture below is called a “flume” in which you can freely control the flow speed. Using the flume, we are studying the detailed effects of flow speed on the feeding behavior of spotted garden eels (Heteroconger hassi) under controlled conditions.
This research is being conducted at the Okinawa Institute of Science Technology (OIST), where researchers from various background work together. This is an
We are investigating the
3D reconstruction of feeding movement consist of tracking body parts and reconstructing 2D videos into 3D. In behavioral studies, animals are usually marked with something distinguishable such as beads and tracked with softwares. However, it is difficult to put markers on garden eels and even if it were possible, you would need to consider the effects of markers on their behavior. In our study, we need to track body features frame by frame which is an endless task if done manually; So we have automated the task using Python package, DeepLabCut, which tracks unlabeled points using deep learning (this package is free!)17,18.
Two of eyes enable us to convert visual information into three dimensions. In 3D reconstruction, multiple cameras are calibrated to track points while recording their relative position to one another. For this purpose, we are using dltdv package in Matlab19.
Even iPhones are suitable for this research!
3D reconstructions of behavior enable us to investigate various parameters in detail, such as time, distance, speed, angle, and the trajectory of a garden eel capturing a prey item. With this detailed behavioral analysis, we are trying to reveal
The figure below shows the movement of a garden eel's face under different flow speeds. Points indicate the location of the face in each frame. You can see that
Previous research has mostly focused on effects of mean flow speeds as a simplification, although more complex flow conditions may happen in the field. Thus, we plan to look into
I'm mainly working on the garden eel project. With an interest in animal behavior, I started the interdisciplinary research investigating effects of flows as a physical factor primarily on garden eels, initiated by Prof. Amatzia Genin. As a first author of the project, I'm conducting not only lab experiments and analysis, but also fieldwork for surveying flow conditions in the habitats. I launched this website to convey interesting facts about garden eels.
Heng is a postdoc in Marine biophysics unit at OIST. She specializes in experimental hydrodynamics with a focus on turbulent boundary layer flows over a rough or porous bed and their impact on biological processes and sediment transport. She takes care of the engineering aspect of the garden eel project, including the fluid dynamics and some image/video processing.
The primary objective of Professor Mitarai’s research is to understand the role of ocean turbulence in regulating biological processes and its consequences for population structure and dynamics of marine ecosystems, through international collaborations. These studies include investigations of larval dispersal via coastal eddies and the role of dispersal in structuring marine populations, understanding biological responses of corals to turbulent flows and their integrated effects on biogeochemical cycling, and impacts of tropical cyclones on particle aggregation and biological pumps. Using his skills and experience as a fluid dynamicist, Professor Mitarai contributes to a new interdisciplinary field in the marine sciences.
Prof. (emeritus) Amatzia Genin is a marine ecologist and biological oceanographer at the Hebrew University of Jerusalem and the Interuniversity Institute for Marine Sciences of Eilat, Israel. His major interest is in the coupling between physical and biological processes in the marine environment, focusing on the effects of water motion on fundamental ecological processes, including predator-prey relationships, competition, symbiosis, mass transfer, and behavior. Since 2020, he is co-supervising Kota Ishikawa for his thesis research.