Dolphin/Porpoise: Dolphins and porpoises are guides to the Underworld and messengers of the dreamworld and of progress. They symbolize joy, playfulness, lack of inhibitions, power, swiftness, the sea, eloquence, magick (specifically water magick), discovery, communication, truth, trust, balance, harmony, breathing, rythm, patterns and relaxation. They are connected to Water and to Astarte, Ishtar, Isis, Apollo Delphinos and sea deities in general.
Fish: Fish symbolize love, fertility, victory over death, healing, prophesy, abundance, wealth, harmony, regeneration, children, pregnancy and bringing love into your life. They are connected to the Moon, to Water, Atargatis, Ishtar, Derceto, Isis, Aphrodite, Freyja, Venus, Dagon, Poseidon and Kuan Yin.
Frog/Toad: Frogs and toads symbolize feminine energy, fecundity, water, new life, new beginnings, the mystery of creation, cleansing, refreshing, purifying, refilling, clearing negativity, replenishment, positive energy, transformation, beginning a new cycle, long life, good luck, changing luck, starting new projects and prosperity. They are a Goddess symbol and are connected to the Moon and Heket, Isis, Hathor, Ch'ing-Wa Sheng, Aphrodite, Sabazius and Ahriman.
Otter: Otters symbolize playfulness, balanced female energy, curiosity, joy for self and others, lack of jealousy and envy, lack of worry, talent, faithfulness, social life and happiness. They are tricksters. They are connected to the elements of Earth and Water and are connected to Cernunnos.
Seal: Seals symbolize playfulness, parenting and protection (specifically protection during travel over water, when changing your life completely, when facing divorce or a traumatic separation form a loved one, and from gossip and danger).
Whale: Whales symbolize elegance, ancient teachings, history, clairaudience, telepathy, psychic abilities, sound and music healing, death and rebirth, initiation, the waters of life, regeneration, the sea, music, longevity, family and friends, learning magick, elelmental magick and trust. Whales are the record keepers. They are connected to Derceto.
(Reproduced from: http://wicca.com/celtic/wyldkat/wkwater.html)