There are 26 types of fish in the large image. Each fish represents a letter, and we can deduce which fish is which letter based on the frequencies of letters in English (up to ambiguities for fish whose numbers are identical).
Number of fish | Letters |
20 | E |
14 | T |
12 | A |
11 | O |
10 | I, N |
9 | H, R, S |
6 | D, L |
4 | C, M, U, W |
3 | F, G, P, Y |
2 | B |
1 | J, K, Q, V, X, Z |
From this, we can determine that the answer, written at the bottom in fish, must match [CMUW][HRS]A[HRS][HRS]E[HRS]. One can deduce that the only plausible English word match is CRASHER.