Search Species
Search for fish species by common or scientific name, or use filters to browse by water type, size, temperament, and difficulty.
Found 665 species
Mabahiss lightfish
Vinciguerria mabahiss
Vinciguerria mabahiss is a tiny deepwater lightfish from the Red Sea that uses rows of photophores (light organs) for counter-illumination - basically a living stealth mode in the midwater dark. Its whole lifestyle is mesopelagic (open-water, deep), so its "care" is really more science-lab territory than home aquarium stuff.
Maejo tiger loach
Rhyacoschistura maejotigrina
Little stream loach with bold tiger-like bars that really pop when it is cruising over rocks in fast flow. It stays small but has a lot of personality for its size, digging around and darting between stones if you give it current and hiding spots.
Maltzan's goby
Wheelerigobius maltzani
This is a tiny West African coastal goby that lives right down on the bottom in warm, shallow inshore water. Its big appeal is the "little predator" vibe - it perches, scoots, and hugs structure like a classic goby, but its real-world habitat is marine shoreline rather than a typical freshwater community setup.
Mandarinfish
Synchiropus splendidus
This is the classic mandarin dragonet-the little reef crawler that looks like someone hand-painted neon blue and orange squiggles onto a fish. It spends basically all day pecking at live rock for tiny pods, and at dusk you can sometimes catch the pair-spawning "rise" if you keep a bonded male/female. Absolutely reef-safe, but it's one of those fish that does amazing only when the tank is truly mature and full of microfauna.
Mandeville's loach catfish
Zaireichthys mandevillei
This is a tiny little Congo River loach catfish that stays about an inch long, with a bold dark collar right behind the head and a speckly pattern. Its basically built for life in moving water - it likes to tuck into sand and squeeze around rocks - so its a super cool "micro-catfish" for a river-style setup if you can actually source one.
Manglolo
Sicydium bustamantei
This is a rock-hugging stream goby from the Gulf of Guinea islands that lives in clear, fast water and sends its larvae out to sea before they return upstream. It scrapes algae and diatoms off stones with its sucker mouth and will clamber around rocks all day, but it almost never shows up in the hobby and really needs a high-flow river setup to do well.
Marlin-spike grenadier
Nezumia bairdii
Marlin-spike grenadier is a deep-sea rat-tail with a long whip tail and big eyes, cruising over soft bottoms on the Atlantic slope. You see it from Newfoundland down to Florida in near-freezing water hundreds of meters down, picking off krill, amphipods, and worms. Super cool to spot on ROV dives, but not a fish for home aquariums.
Marquesas dwarf flounder
Engyprosopon marquisense
This is a tiny deepwater lefteye flounder from the Marquesas Islands - one of those little sand-hugging ambush fish that looks like a leaf until it moves. Super cool biologically, but honestly not a realistic home-aquarium fish since it comes from 108-408 m depths and there is basically no established hobby care info for the species.
Marsh Yunnan loach
Yunnanilus paludosus
A neat little stone loach from marshes in Yunnan, China, it tops out around 3 inches and spends its time nosing through plants and leaf litter for tiny critters. It is a coolwater, subtropical fish from calm vegetated marshes rather than a high-flow hillstream, so it appreciates gentle flow, clean water, and a soft sandy bottom. Keep a small group and it will settle in nicely once it feels safe.
Masked julie
Julidochromis transcriptus
This is a little Lake Tanganyika rock-dweller with bold black-and-white striping and that cool dark "masked" face. Give it a pile of rocks and tight caves and it will cruise around like it owns the place, especially once it pairs up. Small fish, big attitude - but in a manageable, "fun to watch" way if you plan the tank around territories.
McCosker's coralbrotula
Ogilbia mccoskeri
This is a tiny, super-secretive little reef brotula from the SW Caribbean that spends its life tucked into coral rubble and crevices. It is a bottom-hugging carnivore that picks off small mobile crustaceans, and you will mostly see it at dusk or when food hits the water. Cool fish, but it is absolutely not a typical aquarium species, so most "care" info out there is guesswork or confused with McCosker's flasher wrasse (totally different fish).
Mekong sheatfish
Kryptopterus paraschilbeides
Kryptopterus paraschilbeides is a small Mekong River sheatfish that does the whole sleek, no-dorsal-fin Kryptopterus look, but its body is more "normal catfish" than the super see-through glass catfish you usually see in shops. In the wild it moves with the flood cycle - heading into flooded forest at high water, then back to the main river seasonally - which is a pretty cool bit of behavior for a little catfish.