From a study by Papoutsoglou SE, Karakatsouli N, Papoutsoglou ES, and Vasilikos G:
The objective of this study was to further investigate the effects of music on fish physiology, bearing in mind available information regarding the involvement of endogenous and exogenous factors in fish farming. Therefore, Cyprinus carpio (50.5 +/- 0.36 g) were reared in a recirculating water system under 80 and 200 lux and subjected to no music at all (control, ambient noise only), 4 h of Mozart’s Eine Kleine Nachtmusik, or 4 h of anonymous Romanza-Jeux Interdits for 106 days. Both music treatments resulted in increased growth performance at both light intensities, with Romanza treatment at 200 lux resulting in better growth performance than Mozart treatment. Furthermore, feed efficiency for the Romanza groups was significantly better than for the control. Although no significant music effect was apparent for brain neurotransmitters, lower anterior intestine alkaline protease levels were detected for both music treatments. [emphasis added] Taking into consideration the numerous advantages of recirculating water systems, it should be emphasised that fish response to music expresses the results of various physiological and biochemical processes, especially when fish notably respond differently when subjected to two different pieces of music. [emphasis added]
Eine Kleine Nachtmusik:
Romanza-Jeux Interdits:
Incidentally, that music is no longer anonymous but has been almost certainly attributed to Fernando Sor. (And I have taken certain editorial liberties in making the titles of songs in the abstract conform to correct editorial standards for quoting titles of entire works.)
As I’ve been saying, not every piece of music is equally good for you, especially in varying circumstances. Mozart is demonstrably better on a number of indices, but a steady diet of 100% Mozart will not be good for you. It’s better to vary your music within the classical range of 800 AD to 1900 AD. Just be aware that not every piece of music is good for you, as has been shown many times in the research. Here we see that carp grow larger and are healthier with exposure to Renaissance, Baroque and Classical guitar music than other kinds of music (be aware that different species respond differently, as well). So choose your music wisely!