Machete

Where they come from

Elops affinis (often called machete, Pacific ladyfish, or just ladyfish) comes from the eastern Pacific coast - think surf zones, lagoons, estuaries, and mangrove-y backwaters from Mexico down into parts of Central America. They cruise in and out with the tides, so they are naturally built for changing salinity and lots of open-water swimming.

That lifestyle tells you most of what you need to know: they are fast, jumpy, oxygen-hungry predators that like room, flow, and clean water. They are not a "cute oddball" for a mixed brackish community. They are basically a skinny little torpedo.

Setting up their tank

If you are thinking "I have a 55" - stop right there. These fish get long, they move nonstop, and they spook hard. The minimum tank that felt even remotely fair for a juvenile group was a long footprint with serious surface area. Bigger is always better with this one.

• Tank size: Plan for a very large, long tank (think 6 ft+). Small tanks turn into smashed noses and constant pacing.
• Lid: Tight-fitting, no gaps. They jump like they are paid to do it.
• Flow and oxygen: Strong filtration and surface agitation. They are open-water fish and hate stale water.
• Salinity: Brackish that you can measure and keep steady with a refractometer (not a swing-arm).
• Layout: Open swimming lanes. Keep decor to the edges. Use smooth stuff, because they will scrape themselves at speed.

Substrate is not a big deal. Sand looks natural and is easy to vacuum. What matters more is stability: heater that can keep up, rock-solid salinity top-offs (brackish still evaporates as freshwater), and filtration that can handle messy feedings.

For salinity, I had the best results keeping them in the mid-brackish range and not bouncing it around. They tolerate change, but they do not thank you for it. Pick a target specific gravity and hold it there with consistent mixing and top-off habits.

What to feed them

They are predators that want meaty foods and they burn calories fast. The trick is getting them onto a routine so they do not go from "fine" to "skinny" before you notice. In my tanks they ate aggressively once settled, but new arrivals can sulk for a bit.

• Staples: silversides, lancefish, smelt chunks, shrimp, squid, marine fish flesh (varied).
• Frozen foods: mysis and krill for smaller juveniles, then larger pieces as they grow.
• Live foods: can be useful to start reluctant fish, but do not build a whole plan around feeders.
• Pellets: some individuals learn them, many do not. If yours takes them, great - still rotate real seafood.

I also recommend soaking frozen foods in vitamins now and then, especially if you are leaning heavily on a couple items. Variety is your friend here. A machete on a narrow diet can start looking hollow behind the head even if it is eating.

How they behave and who they get along with

They are active, nervous, and very aware of motion outside the tank. Mine were way calmer in a group, but that also means you are committing to more tank and more food. Solo fish can be jumpier and spend more time doing laps.

Tankmates are mostly about size and speed. If it fits in their mouth, it is food. If it cannot compete at feeding time, it is going to starve. Slow brackish favorites (scats, monos, archers) can get outcompeted unless you are really on top of feeding strategy.

• Good candidates: other large, fast brackish/marine-leaning fish that can handle strong flow and aggressive feeding.
• Bad candidates: small fish, slow fish, long-finned fish, or anything timid.
• Inverts: do not expect shrimp/crabs to last.

Breeding tips

Breeding in home aquariums is basically a non-starter. In the wild they spawn offshore and the larvae (leptocephalus stage) drift and develop in ways that are not realistic to replicate in a typical fishroom. If someone tells you they bred them in a normal brackish setup, I would want receipts.

If your goal is breeding projects, pick a different brackish fish. If your goal is keeping a cool, challenging predator healthy long-term, focus on space, water quality, and diet.

Common problems to watch for

• Jumping and impact injuries: the big one. Tight lid, calm environment, and enough swimming room help a lot.
• Refusing food after shipping: give them dimmer light at first, keep the tank quiet, offer smaller meaty items, and do not chase them with nets.
• Skin damage and secondary infections: often from panic darts into decor or glass. Keep hardscape smooth and open.
• Parasites from live foods or wild-caught stock: quarantine is your best friend with this species.
• Rapid weight loss: they can look fine and then suddenly look like a knife. Increase feeding frequency and vary foods.
• Nitrate creep from heavy feeding: big water changes and serious filtration, otherwise they get run down.

If you keep salinity consistent, keep the water moving and clean, and give them a long runway to swim, they are hardy in their own way. But they are unforgiving if you cut corners. This is one of those fish where the tank has to be built around the fish, not the other way around.