Beach silverside
Atherinella blackburni
Beach silversides have a slender, elongated body with a prominent silver stripe running along each side and translucent fins.
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About the Beach silverside
This is a little coastal silverside that cruises the shallows in loose groups and flashes like a tiny chrome dart when the light hits it right. In the wild it hangs around beaches, estuaries, and lagoons, picking at small drifting foods in the surf zone. It is cool, but its real "gotcha" is that it is an open-water, salt-tolerant schooling fish that does best in bigger, well-oxygenated setups rather than a typical planted community tank.
Also known as
Quick Facts
Size
13 cm
Temperament
Peaceful
Difficulty
Advanced
Min Tank Size
30 gallons
Lifespan
2-4 years
Origin
Western Central Atlantic (Mexico to northern Brazil)
Diet
Carnivore/micro-predator - zooplankton, tiny crustaceans and insect larvae; in tanks, small frozen foods and fine pellets
Water Parameters
22-28°C
7.5-8.5
8-25 dGH
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Calculate heater sizeCare Notes
- Give them long, open swimming room and a tight lid - beach silversides are missiles and will jump through the tiniest gap when spooked.
- This species occurs in coastal shores and estuaries; if kept, maintain stable estuarine-to-marine conditions appropriate to its collection locality rather than relying on a single universal SG target.
- They hate stale water and low oxygen, so crank surface agitation (powerhead or strong filter return) and keep temps in the low-to-mid 70s F if you can.
- Keep them in a proper group (6+), or they get twitchy and smack into glass; a bigger school spreads aggression and they color up and feed better.
- They are picky about food size and movement - start with small frozen/live stuff (baby brine, copepods, finely chopped mysis) and train onto tiny pellets gradually.
- Tankmates: think fast, brackish, and not mouthy - avoid big puffers, scats/monos that will outcompete them, and anything that fits them in its mouth.
- Watch for "nose rub" and torn fins from panic dashes; dim the lights, add floating cover, and avoid sudden movements around the tank.
- Breeding is doable if you feed heavy and give them spawning mops or fine plants; they scatter sticky eggs, so pull the mop/eggs or the adults will snack.
Compatibility
Good Tankmates
- Other small schooling brackish fish - more silversides, brackish gobies that stay mid to bottom, and similar fast little swimmers. Beach silversides are way more relaxed when they have a proper group and tank mates that move like they do.
- Bumblebee gobies (Brachygobius spp.) - they hang out low, dont bother the silversides, and the silversides ignore them. Just make sure the gobies are actually eating (frozen/live) so they dont get outcompeted at feeding time.
- Knight goby (Stigmatogobius sadanundio) - works in a roomy brackish setup if the knight is not huge. They are mostly bottom-territorial, while silversides stay up in the water column. Give caves and line-of-sight breaks.
- Mollies (Poecilia sphenops/latipinna types) acclimated to brackish - tough, active, and they handle the same salt range. They match the silversides energy and dont get stressed by the constant midwater motion.
- Figure 8 puffers (Dichotomyctere ocellatus) - only if you have a big tank and a well-fed, not-mean individual. Some are fine with fast schooling fish, but it is a gamble. I would only try it with a backup plan because puffers can randomly decide fins look like snacks.
- Small scats (Scatophagus argus) - in a large brackish grow-out, scats are usually too busy grazing to mess with silversides, and the silversides are quick enough to stay out of the way. Watch size though, because scats get big and will eventually own the tank.
Avoid
- Anything nippy - tiger barbs, serpae tetras, most fin-nippers in general. Silversides are peaceful and spend all day in open water, so they are basically inviting trouble from fish that like to harass moving targets.
- Big predators that see them as feeder fish - larger archerfish, snook-ish/brackish predators, big cichlids, large catfish. Beach silversides are slim, mouth-sized, and they swim in the open, so predatory tank mates will eventually cash that check.
- Slow fish with long fins - bettas, fancy guppies, angelfish, slow gouramis (plus most of these are not brackish anyway). Even if the silversides are not aggressive, their constant zipping around stresses slow, frilly fish and feeding time turns into a mess.
Where they come from
Beach silversides (Atherinella blackburni) are little coastal speedsters. In the wild they hang around shorelines, surf zones, lagoons, and estuaries where salt and fresh mix and the water can change fast with tides and rain.
That background explains why they are tough in some ways (they can handle swings) and maddening in others (they do best in a big, well-oxygenated tank and they do not like being cooped up).
Setting up their tank
Think of these as open-water schooling fish, not decor fish. Give them length more than height. They use every inch and they panic-bolt if they feel trapped.
- Tank size: I would not do less than a 40 breeder for a small group, and a 75+ is where they start looking relaxed.
- Group size: 8-12 is a good starting point. Fewer and they act jumpy and beat each other up more.
- Filtration: strong turnover plus extra aeration. A canister or big HOB with a powerhead/wavemaker is your friend.
- Flow: moderate to brisk, with a calmer corner so they can rest.
- Substrate/decor: sand or fine gravel, rocks or driftwood kept to the sides to leave a long runway for swimming.
Lid it like you mean it. They jump. Any gap around cables or filters will eventually be the gap they find.
For brackish, I have the best luck keeping them in the low-to-mid range rather than bouncing around. Something like 1.005-1.012 specific gravity works for a lot of setups, but pick a target that matches your stock list and stick with it. Mix marine salt in a bucket, never add salt straight to the tank.
- Temperature: mid-70s F is a comfortable middle ground for most home tanks.
- pH/hardness: they are usually happier in harder, more alkaline brackish water than soft/acidic water.
- Maintenance: frequent small water changes beat occasional big ones, especially if you feed heavy (and you will).
Keep the lights a bit broken up with floating plants or surface cover, and give them a dark background. It sounds cosmetic, but it really cuts down on spooking and glass surfing.
What to feed them
These guys are constant pickers in the water column. If you try to run them on one big feeding a day, they look skinny and get edgy. I do small meals 2-4 times a day when I can.
- Frozen: brine shrimp, mysis, calanus, chopped krill (sparingly), finely chopped clam or shrimp.
- Live (great for settling new fish): adult brine, blackworms, copepods, daphnia if you can get it.
- Dry: small floating or slow-sinking pellets, fine flakes. Use as a base once they recognize it as food.
New imports sometimes ignore pellets at first. Start with frozen/live to get weight on them, then mix in dry food gradually so they learn the routine.
Watch their bellies. A healthy school looks sleek but not pinched. If you see hollow bellies or stringy white poop, slow down and troubleshoot before you just feed more.
How they behave and who they get along with
They are peaceful in the sense that they are not looking to bully other species, but they are high-strung and fast. Most problems are stress problems: not enough space, not enough schoolmates, or tankmates that make them nervous.
- Best tankmates: other calm brackish fish that like similar salinity and are not fin-nippers.
- Avoid: aggressive cichlids, fin-nippy fish, and anything big enough to treat them like live snacks.
- Also avoid: very slow, delicate fish that get outcompeted at feeding time.
They do a tight schooling display when they feel secure, and it is honestly the whole point of keeping them. If they spend the day hiding in corners, something in the setup is off.
If you want them calm, add more silversides before you add more species. A bigger school fixes a lot of behavior issues.
Breeding tips
Breeding can happen in home tanks, but it is not like livebearers where you wake up to babies. They are egg scatterers and adults will happily snack on eggs and larvae if they find them.
- Spawning triggers: heavy feeding plus slightly warmer water and longer photoperiod often gets courtship going.
- Egg placement: they like fine-leaved plants, spawning mops, or filamentous algae to stick eggs to.
- Saving eggs: move the mop/plant to a separate rearing tank, or use a divider/egg trap setup.
For fry, think tiny foods from day one. Rotifers or very small live foods are usually needed at first, then newly hatched brine as they grow. Clean water matters a lot because you will be feeding often.
Do not count on fry surviving in the main display. If you want to raise any, plan for a separate small rearing tank and live foods ahead of time.
Common problems to watch for
- Jumping: almost always happens during the first week, after a scare, or during chasing. Tight lid and dimmer light help.
- Wasting/skinny fish: often from internal parasites or not getting enough frequent food. Quarantine and deworming are sometimes needed for wild fish.
- White spot-like issues: can show up after stress or temperature swings. Treat in quarantine when possible and stabilize the tank first.
- Mouth/nose injuries: they slam glass when startled. Reduce sudden light changes and keep the front glass clear of reflections.
- Rapid breathing: usually low oxygen, high ammonia/nitrite, or a salinity mismatch. Add aeration immediately and test water.
If you see them gasping at the surface, do not wait. Add air, increase surface agitation, and check ammonia/nitrite right away. Brackish fish still burn fast in bad water.
My biggest takeaway with beach silversides: they reward big tanks, big groups, and lots of oxygen. Get those three right and most of the other stuff becomes routine.
Similar Species
Other brackish peaceful species you might be interested in.
African moony
Monodactylus sebae
This is that shiny, diamond-shaped "mono" that cruises around in a tight pack and looks like a little silver dinner plate with black bars when it's young. The big thing with African moonies is they're euryhaline-so they'll tolerate freshwater as juveniles, but they really shine long-term in brackish (and can be transitioned toward marine as they mature). Give them a big, open tank and a group, and they turn into nonstop, super fun midwater swimmers.
American shadow goby
Quietula y-cauda
This is a little mudflat goby from California down into the Gulf of California that loves hanging tight to the bottom and vanishing into burrows. The neat tell is that sideways Y-shaped blotch right at the base of the tail, plus the row of dark spots along the side. Its whole vibe is brackish estuary life - calm water, soft substrate, lots of hiding holes.
Banded-tail glassy perchlet
Ambassis urotaenia
This is one of those see-through glassy perchlets where you can literally watch the organs shimmer when it turns-super cool in the right lighting. In the wild it hangs around river mouths and mangroves and cruises in groups, so it does best when you keep a little gang of them and give them some open swimming room.
Barbed pipefish
Urocampus nanus
Urocampus nanus is a skinny little pipefish from sheltered seagrass and estuary areas around southern Japan and nearby coasts, where it hangs out down low among eelgrass. The really wild part is the males brood the eggs in a pouch under the tail and give birth to fully formed mini pipefish. Its care is basically "pipefish rules" - calm tank, lots of live/frozen tiny meaty foods, and tankmates that will not outcompete it at feeding time.
Buffon's river-garfish
Zenarchopterus buffonis
This sleek, surface-dwelling halfbeak has a distinct dark stripe along the snout and is typically found at the surface in coastal waters, estuaries, and rivers where it feeds on terrestrial insects. In aquaria it does best with floating/surface foods and a secure cover, and it requires brackish (or marine) conditions long-term. Reproduction is internally fertilized; FishBase lists the species as ovoviviparous.
Cuban cusk-eel
Lucifuga subterranea
This is one of Cuba's weird, wonderful cave brotulas - pale, blind, and built for cruising around in dark cave pools and sinkholes. It is a livebearer (yep, it gives birth to fully formed young), and it hunts small crustaceans in those underground waters.
More to Explore
Discover more brackish species.
Atlantic Mudskipper
Periophthalmus barbarus
This is that wild little amphibious goby that straight-up climbs around on land like it forgot it was a fish. They've got big googly eyes, tons of personality, and they'll perch, hop, and patrol their territory-honestly more like a tiny crabby lizard than a "regular" aquarium fish.
Banded Archerfish
Toxotes jaculatrix
This is the fish that literally spits jets of water to knock insects off branches-watching one "take aim" is unreal. They're super aware of what's going on outside the tank and will even learn to beg and snipe food from the surface once they settle in. Give them height and some open swimming room and they act like little aquatic sharpshooters.
Barred mudskipper
Periophthalmus argentilineatus
This is one of those classic "walks around like it owns the place" mudskippers-big goofy eyes, climbs, hops, and spends a ton of time out on the mud when it's humid. In the wild it lives on intertidal mangrove/nipa mudflats and even shuttles between little pools and open air, hunting worms, insects, and small crustaceans. It's super fun to watch, but it really wants a brackish paludarium setup (not a normal aquarium).
Blotched eelpout
Zoarces gillii
Zoarces gillii is a cold-temperate eelpout from the Northwest Pacific that hugs the bottom over sandy-mud inshore areas and even pushes into estuaries. It's got that long, eel-like body and a sneaky, sit-on-the-bottom predator vibe - very much a cool-water, brackish-to-marine oddball rather than a typical tropical aquarium fish.
Bumblebee goby
Brachygobius doriae
Brachygobius doriae is one of the classic "bumblebee gobies" - tiny, bottom-hugging little characters that perch on rocks and sand and stare at you like they own the place. They're at their best in a calm setup with lots of caves and leaf litter, and they really shine once you get them eating frozen/live foods reliably (they're slow, picky eaters). Also: they're one of the species that gets mislabeled a lot in shops, so it's super common to see them sold under the wrong bumblebee-goby name.
Bumblebee goby (Bumblebee fish)
Brachygobius xanthozonus
This is that tiny little goby with the bold black-and-yellow bands that likes to perch on the bottom and stare back at you like it owns the place. It's happiest in lightly brackish water with lots of little caves and sight-breaks, and it's one of those fish that often refuses flakes-frozen/live meaty foods usually flip the "yes, I will eat" switch.
Looking for other species?