In many fish species, group formation has been shown as important behavioural strategy to increasing the individual fitness. Previous work of Fischer & Hofmann (2004) as well as Fischer & Reyjol (2006) clearly demonstrated, that group formation especially in nocturnal benthic fish species significantly increase foraging efficiency (fig.1), reduces predation risk (fig2) and finally may lead to a significant increase in somatic growth.

Such a performance enhancement implies, that group members do exchange information among conspecifics, leading to an individual advantage compared to solitaire living fish. Besides optical and chemical communication, it is well known that many fish, i.e. cod species (fig. 3) but also many others (in total > 1000 species) do communicate on an acoustic basis (Rountree 2003).

So far known reasons for sound production in fish are:

• Aggression (to defend resources against conspecifics or other species)
• Spawning activity (courtship behaviour)
• Foraging (to enhance intraspecific foraging success)
• Schoaling and group adherence (to reduce predation risk)
• Warning signals (intraspecific communication)

In a joint project together with the University of Applied Science (Prof. Dr. Steffen Reith / Jakob Klaus-Stöhner - B.S.) and the BAH research aquarium (Dr. Emanuel Hensel), we perform lab experiments (fig. 4a,b) on diel patterns of acoustic communication in fish. Using the sea robin (Trigla lucerna) (fig. 5) as model organism for acoustic active fish, we actually work on the following questions/topics:

1. Together with the department "Theoretische Informatik" of the University of Applied Science in Wiesbaden, we develop computer algorithms to automatically discriminate biological relevant fish sounds from noise? (Bachelor thesis Jakob Klaus-Stöhner; Untersuchung zur Bioakustik bei Fischen am Beispiel des Knurrhahns (Trigla lucerna)).
2. In lab experiments, we focus on patterns of sound production in Trigla lucerna over the diel cycle (fig. 6). For this, we record the sound production and the behaviour of the fish by hydrophones and video cameras over 24h to link sound production an individual behaviour (fig. 7). (Bachelor thesis Kristin Trentsch - TU Dresden; Tagesperiodischer Aktivitätsrhythmus und intraspezifische Interaktion bei Knurrhähnen (Triglidae) & Bachelor thesis Robin Lenz Uni Konstanz; Die Bedeutung intraspezifischer akustischer Kommunikation für das Gruppenverhalten des Roten Knurrhahns (Trigla lucerna)).

 Our next steps in this project are:

1. Together with the department "Theoretische Informatik" of the University of Applied Science in Wiesbaden, we try to significantly increase the speed of data processing of the sound and video records. A main problem in the analysis of our sound and video records of these experiments is the still slow processing speed of the huge amount of sound and video data collected per day (in average > 8 GB per 24 hours). To efficiently analyse these data on biological relevant sounds incl. video sequences, specific computer algorithms are developed to finally allow a first and reliable online pre-screening of the data on fish sounds followed by a second in depth analysis of the interesting sequences.
2. In further lab experiments (beginning in February 2011), we will use a new technology to locate the sound origin within the experimental aquaria by acoustic triangulation (fig. 8). This step is most important to identify the fish in the group which have produced the sound at a specific time. This step will finally allow us to identify bi-directional communication among different group members. Based on this technique, we  perform in-depth experiments on intraspecific behaviour and information transfer among group members.