Eine Kleine Yachtmusic – some fishy research

Rainbow trout

You might remember the famous salmon study by Bennett et al. (2009) (pdf), the classic demonstration of why corrections for multiple comparisons are vital in fMRI research. Yes, the one where the researchers found significant activation in parts of a salmon’s brain. Dead salmon’s brain to be exact.

Well, the trouts are back in town. This time the rainbow variety, and the study is about the good old Mozart effect.

I have absolutely no expertise in the field of fisheries and these kinds of studies, but sometimes the keyword-trawler fleet hauls in some unexpected catch: in this paper, a group of scientists in the University of Athens have studied the effects of playing music to rainbow trouts in a fish farm.

Does this sound silly? Sort of springs to mind the Fish Slapping Dance from Monty Python? It does not help that they cite papers by Fish (1972) and Bass & Ladich (2008) in their intro… But this is a serious scientific study and here’s why.

Over-fishing is one of the major threats to our environment and our future. It has been estimated that we’ve lost 80% of the marine biomass during the last century, 60% in just the last 40 years.

Fish stocks are a crucial source of nutrition for humans, and as the natural stocks are dwindling, fish farming becomes more important in feeding the world. Fish farms are far from unproblematic, though. There are ethical issues about animal well-being, and many fish farms pollute as fish feed and waste is flushed from the farm to the environment. These flow-through and net cage systems are basically huge plastic bags set up in the sea, keeping the fish inside but letting the water flow through. A newer alternative to these are the recirculating water systems (RWS). These are large fish tanks or pools that are not connected to the natural water bodies, and have a closed circulation of water, with only a little fresh water added, like a swimming pool. The ethical issues remain, but environmentally this is better as the impact to natural water bodies is limited and these can be situated closer to the consumers rather than at the coast, so this could cut down transport costs and further lower the environmental impact of fish. Also, being closed-circuit, they are ideal testbeds for research, as all variables can be controlled by the experimenters.

However, fish adapted to live in the ocean do not adapt easily to living in tanks. People have been tweaking the colour of the tanks, lighting, light cycles, feed etc. to make e.g. rainbow trouts to grow in the RWS’s, and like in any attempts to make an environment more cosy and home-like, at some point it comes to putting on some nice music. Mellow tones might alleviate the stress induced by the close quarters.

Noise pollution is a serious issue for the well-being of marine life, so it could be that a pleasant sound environment could have a positive effect on it.

The researchers have done prior research on the effects of music on fish, and the “Mozart K525”, also known as Serenade in G, “Eine Kleine Nachtmusik” has been their favourite piece to do the tests on. In this study, they used the second movement (Romanze – Andante) and to see if there is some magic juice specifically in Mozart’s music, they used also another Romanza, by the most prolific composer of them all: Anon.

The rainbow trout can indeed hear sounds, although their range of hearing stops at around 400Hz, which basically leaves out much of what is “music” in the stimulus. The authors decided to utilise white noise as a control condition, “in order to determine whether the effects observed could be attributed to music per se and or merely to the presence of a novel acoustic stimulus within the experimental environment”.

I’m no expert on fish hearing, but I would not necessarily call white noise as “novel acoustic stimulus”. Perhaps just bursts of white noise to mimic the rhythm of the music would have been a control condition that would actually answer the question if there’s some specific effect that music has? A scrambled version of the music? Although, it has to be said that the music conditions are not much different from the noise if you only hear frequencies up to 400Hz. This is what a sample of Mozart K525 that was fed through a lowpass filter with a cutoff frequency of 400Hz sounds like:

(The original by Sir Neville Mariner and the Academy of St Marlin in the Fjord)

The stimulation was set to hefty 140dB levels, to be about 100 times louder than the regular 121dB sound in the experimental tanks (I assume produced by the movements of the fish and the filtering systems etc.). This is way beyond the pain threshold of human ears, but here the sound waves are generated in the water, so the numbers are not directly comparable. The sound stimulation was applied for 4 hours a day during weekdays (the fish got time off on weekends) and lasted for 98 days.

The catch of the day: luckily no fish died during the experiment. After the experiment, though, all trouts were decapitated and dissected. Their brains were frozen so that neurotransmitter analysis could be carried out. Also the livers, spleens and digestive tracts were harvested for analysis.

The fish in tanks that listened to either of the Romanzas, had higher body weights than the fish in the control tanks, and especially the fish who heard the Romanza by Anon were longer than the rest. Also, the fish who listened to the 140dB low-pass filtered Mozart had higher brain serotonin and lower dopamine levels than the rest, suggesting that they were more relaxed than the others.

The authors conclude: “Appropriately applied music transmission supports both the achievement of the optimum homeostasis level of farmed fish as well as, predictably, of their “happiness” and, by extension, of a beneficial-healthy and advantaged aquatic and terrestrial environment, especially as regards use of recirculating water systems, the sum total of these achievements resulting in the producer’s satisfaction and profit.”

I’m not sure what to say about this. In this study the amount of food that was administered to each tank depended on the weight of the fish. So the musically stimulated tanks started receiving more food as the fish in them started to slowly but surely outgrow their peers. So the added weight in the end is explained by the increased feeding, weight does not come from thin air (or water). Thus the interesting question is, what sets the musically stimulated tanks into a different growth trajectory in the first place? Periodic and predictable sound stimulation could have some beneficial effects on growth rates, perhaps through some effect of lowering the stress levels in those tanks. Finding the roots of this effect would be useful. If it is something in the music per se, it might just be the rhythm – not much else of it survives when transmitted under water and through the auditory system of the Oncorhynchus mykiss.

ResearchBlogging.orgPapoutsoglou, S., Karakatsouli, N., Skouradakis, C., Papoutsoglou, E., Batzina, A., Leondaritis, G., & Sakellaridis, N. (2013). Effect of musical stimuli and white noise on rainbow trout (Oncorhynchus mykiss) growth and physiology in recirculating water conditions Aquacultural Engineering DOI: 10.1016/j.aquaeng.2013.01.003

(Picture of rainbow trout by USFWS Pacific in Flickr. (CC-BY-2.0)

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