Although a number of fish species have been studied in their freshwater life stages, further research on the behavior and habitat requirements of ocean-going fish is required. While fishes have historically been regarded as more “primitive” than other vertebrate groups, Rodriguez et al concluded that several memory and learning systems of bony fishes are noticeably similar to those of reptiles, birds, and mammals. When animals as small and under appreciated as fish display complex mating systems, parental care, and demonstrate the ability to traverse significant distances using olfactory and celestial cues, it is clear that previously established definitions of intelligence should be revisited.
The Humane Society of the United States, "About Fish" (2014). Aquaculture, Fish, and Fisheries. Paper 1.