While you may not ever be able to discuss the nature of consciousness with your goldfish, you may in fact be able to find out how that hot date went, if Art Myrberg's work on fish "talk" continues. As it turns out, his reseach, which began in 1981, and subsequent research by himself and others indicates that fish use sound to communicate.
While it has been known for some time that fish are capable of producing sound, there was no reason to think that it would be communicative in nature. It was believed by researchers generally that only the higher-order aquatic animals, such as dolphins and whales, used sound as a method of exchanging information. Myrberg's work with the bicolor damselfish (Pomacentrus partitus) changed that picture completely. By recording the sounds these diminuitive fish make, and playing them back into the tank, Myrberg has been successful in stimulating the fish to display courtship and protective behaviors, and to either avoid or move toward specific locations within the tank.
Myrberg's research opened the door for other work involving how fish produce sound and what exactly they are talking about. In addition to banging their heads against objects in their environment, a sound production technique favored by fish such as the mottled sculpin, there are three bodily structures fish employ to generate sound. Low-frequency sounds can be produced by vibrating muscles attached to the swim bladder, for fish which possess this organ. Higher-frequency sounds can be made by teeth-grinding or scraping, or by a process similar to how a cricket makes sound: rubbing (stridulation) of the pectoral fins.
Myrberg's work with the damselfish indicates that there is a close analogy between the function of damselfish "vocalization" and birdsong; there are clear signals identifying intruders and strangers, and territorial vocalization has been identified. Female damselfish also show attraction to certain sounds produced by the male, and even though courtship displays are primarily visual, a sonic component is important.
Nellison (1991) and Bleckmann (1993) continued this line of research in testing the hypothesis that low-frequency sound modulation produced by close-proximity body vibration was essential in provoking certain piscine behaviors. Followup work by Satou and others (1994) indicates that such behavior by female hime salmon is instrumental in introducing spawning behavior in the male. Work is currently in progress with guppies, sticklebacks, and green swordtails, all of which appear to incorporate some form of sonic communication in their interactions.
There is no doubt that visual and chemical techniques of communication are those most favored by fish, but sound cannot be ignored, and it promises to provide a unique insight into fish behavior at all scales, no pun intended.
For further reading
Sound production of Oreochromis mossambicus (Mozambique tilapia) - http://www.blackwell-synergy.com/links/doi/10.1046/j.1095-8649.2003.00054.x/abs/
Technique for recording fish sounds in a small tank - http://biology.uky.edu/Yan/Small_tank.pdf
Courtship and mate choices in fishes: integrating behavioral and sensory ecology - http://biology.uky.edu/Yan/sensory_ecology.pdf
"Fish Chatter", Equinox, May/June 1987