Silver splitfin

Where they come from

Silver splitfins (Verilus cynodon) are one of those fish you usually run into through other serious marine keepers, not at the average shop. The ones I have kept were collected around rocky coastal reefs where surge, bright light, and lots of tiny crustaceans are the norm. That background explains most of their quirks in a tank: they like flow, they like to pick all day, and they do not forgive sloppy water.

Setting up their tank

If you want these to last, think "high-energy reef edge" more than "calm lagoon." They do best in mature systems that have been running a while and already have microfauna to graze on. Fresh setups with sterile rock usually end in a slow fade.

• Tank size: I would not bother under 75 gallons for a small group. Bigger is easier because they are active and you get more stability.
• Aquascape: lots of rock with cracks and ledges, plus open lanes for swimming. They use cover, but they are not cave fish.
• Flow and oxygen: strong, varied flow and good surface agitation. If your fish ever hover and "pant" in the current, treat that as a real warning sign.
• Filtration: oversized skimmer, aggressive mechanical filtration, and a plan for nutrients (refugium, algae scrubber, or very consistent water changes).
• Lighting: reef-level lighting is fine. They are not light-shy, but they spook less if you give them shaded zones under overhangs.
• Cover: tight lid. They can launch when startled, especially the first couple weeks.

Aim for reef-typical parameters and keep them steady. I run 1.025-1.026 salinity, 76-78F, and avoid big daily pH swings by keeping gas exchange strong. Stability beats chasing numbers.

What to feed them

They are constant pickers with a real preference for meaty microfoods. In my tanks, the quickest way to get weight on them is frequent small feedings rather than one big dump of food.

• First foods that usually work: live or enriched frozen copepods, baby brine (enriched), mysis (smaller pieces), finely chopped shrimp, and roe.
• Prepared options: high-quality small pellets can work, but many ignore them at first. I have the best luck mixing pellets into a slurry of thawed frozen so they accidentally learn pellets are edible.
• Feeding rhythm: 2-4 small feedings a day is not overkill for this species. An auto-feeder plus one frozen feeding is a nice combo once they accept dry.
• Extras: a thriving pod population in the rock helps a lot, especially for new arrivals.

How they behave and who they get along with

They are alert, fast, and a little pushy around food, but not usually murderous. The biggest issue is that they get outcompeted or bullied by the wrong tankmates, and they hate being the only one of their kind.

• Group size: keep 3-6 if you can. Singles tend to stay on edge and feed worse.
• Good tankmates: peaceful to semi-peaceful reef fish that will not hog every bite (smaller wrasses, chromis that are not jerks, firefish in larger tanks with lots of cover, gobies, tangs that are not overly aggressive).
• Avoid: aggressive damsels, big dottybacks, triggerfish, and anything that makes feeding a contact sport.
• Inverts: generally reef-safe in the usual sense, but they will absolutely hunt tiny shrimp and snack on pods. Decorative microfauna is food to them.
• Corals: no special coral drama in my experience, but they can knock things if the rockwork is cramped and they are spooked.

Breeding tips

Breeding in home aquariums is possible but not something I would call repeatable for most people. Spawning tends to happen when the fish are well-fed, the tank is stable, and there is a clear "seasonal" cue like a slight temp swing or heavier feeding for a few weeks.

• If you want to try: keep a group with a clear pair forming, feed heavy on small meaty foods, and maintain very clean water despite the feeding.
• Spawning sites: they seem to prefer rock faces and crevices in higher flow areas.
• Egg and larval reality check: if they broadcast or leave eggs exposed, they usually get eaten in a community reef. A dedicated setup and larval food plan (rotifers, then copepods) is basically mandatory.
• Best practical approach: if you see courtship, consider moving the group to a breeding tank or removing other fish rather than trying to "save" eggs in a full reef.

Common problems to watch for

They are one of those expert fish where the problems are usually husbandry-related, not random bad luck. Catching issues early is the difference between a quick turnaround and a slow decline.

• Slow starvation: shows up as a pinched belly, hollowing behind the head, and less interest in grazing. Fix by increasing feeding frequency and offering smaller, more enticing foods (pods, roe, enriched baby brine).
• Shipping stress and refusal to eat: common with new imports. Dim lights, strong oxygenation, and quiet surroundings help. I like to start with live/enriched foods to get the first bites.
• Aggression at feeding time: they can get nippy in tight spaces. Spread food out, use a feeding ring on one side and broadcast on the other, and avoid keeping them with aggressive gluttons.
• Crypt and velvet sensitivity: treat any "dusty" look, flashing, rapid breathing, or hanging in flow as an emergency. Quarantine is your friend here.
• Jumping: almost always in the first days or after a big scare. Lid every gap, including around plumbing.
• Parameter swings: they show stress fast if salinity or temperature bounces. Top-off failures are a classic way to lose them.