Detection of fish passing through a narrow path using reflected and transmitted ultrasonic waves

Abstract

The properties of echoes and transmitted waves from a fish body, in megahertz bands, were investigated to construct a fish detection method in a narrow path by a simple measurement structure using a pair of transducers. Experiments were performed in a water tank using dead Japanese jack mackerel (Trachurus japonicus). From the echoes, the outlines of fish could be observed. High amplitudes of echoes from the swim bladder and fins were observed, while relatively low amplitudes of echoes were observed from other body parts, e.g., the head, body surface, and vertebral columns. From the transmitted waves, decreased amplitudes and times-of-flight in waves transmitted from the fish body were observed. The fish could be detected using ultrasound, in megahertz bands, and the combined use of the echo and transmitted waves could increase the information obtained about fish compared with the use of echoes only.

Detection of free-swimming fish passing through a narrow passage using MHz-band ultrasonic reflected and transmitted waves

“…The increases in amplitude and the number of peaks in the echoes and the decreases in amplitude and ΔTOF in the backwall echoes and transmitted waves were observed in each of the nine and five passing events of fish samples 1 and 2, respectively. These results obtained from free-swimming goldfish appeared to show a similar pattern to those we obtained previously using dead Japanese jack mackerel, 31) despite the smaller size of goldfish compared with jack mackerel. This experiment has shown for the first time that backwall echoes can be affected by fish, as observed in the transmitted waves.…”

“…[39][40][41][42][43] We observed decreased amplitude and time-of-flight (TOF) in waves transmitted through a fish's body. 31) Our earlier findings therefore showed that fish can be detected using MHz-band ultrasound, and the combined use of echoes and transmitted waves can increase the amount of information obtained about fish compared with the use of echoes only. However, in our previous study we used dead Japanese jack mackerel, Trachurus japonicus, for our experiments; the validity of this type of measurement for freeswimming fish has not yet been verified.…”

“…In a previous study, we used MHz-band ultrasound to investigate the properties of echoes from a fish's body, from tail to head, and the outlines of fish could be observed. 31) Using MHz-band ultrasound, we observed echoes not only from the swim bladder, which is responsible for 90% of the reflected echoes when low-frequency ultrasound is used, 38) but also from other body parts such as the head, body surface, vertebral columns, and fins. 31) In addition, in our previous study we investigated the properties of waves transmitted through a fish's body; transmitted waves have previously been used for the nondestructive inspection of steel billets.…”

“…31) Using MHz-band ultrasound, we observed echoes not only from the swim bladder, which is responsible for 90% of the reflected echoes when low-frequency ultrasound is used, 38) but also from other body parts such as the head, body surface, vertebral columns, and fins. 31) In addition, in our previous study we investigated the properties of waves transmitted through a fish's body; transmitted waves have previously been used for the nondestructive inspection of steel billets. [39][40][41][42][43] We observed decreased amplitude and time-of-flight (TOF) in waves transmitted through a fish's body.…”

“…To develop a simple method to measure and observe fish behavior, we previously explored the effectiveness of a pair of transducers with MHz-band ultrasound to detect the bodies of fish in a narrow path. 31) Measurement, even in a narrow path, can be useful for counting the number of fish passing through fish pumps, fishways, set-nets, etc. [32][33][34] Although cameras can be used to measure fish behavior in these relatively narrow areas, fish cannot be observed if the environment is turbid or dark.…”