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How Big Do Sea Monkeys Get? (And Factors That Impact Growth)

How Big Do Sea Monkeys Get? (And Factors That Impact Growth)

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The purpose of this blog is to share general information and is written to the author's best knowledge. It is not intended to be used in place of veterinary advice. For health concerns, please seek proper veterinary care. In addition, as an Amazon Associate I earn from qualifying purchases.

For more than 60 years’ sea monkeys have been fun, novelty pets. They look nothing like monkeys, and their popularity has mainly been attributed to some rather creative marketing strategies.

Fully grown Sea Monkeys are approximately half an inch in length. They are sometimes advertised as able to reach an inch in size, but claims are often exaggerated. These fascinating creatures start life as minuscule eggs, known as cysts, that appear to spring to life in water.

The tiny size of sea monkeys is often disappointing to excited kids who may imagine impressively sized swimming primates. But if you know what to expect when you get a sea monkey kit, they can be delightfully entertaining despite their small size.

How Big Do Sea Monkeys Get?

Many Artemia Brine Shrimp Against a White Background

It seems that just everything about sea monkeys has been blown out of proportion, including many claims about their size.

Comic books advertising from the 60s and 70s had entire generations of kids believing that they could instantly grow small communities of naked human-like aquatic creatures inside of a fishbowl.

The term Sea-Monkeys is itself a clever marketing strategy for a cleverly modified form of brine shrimp, called Artemia NYOS. These hybrid shrimp were developed in the late 1950s by Harold von Braunhut after a rise in the popularity of ant farms.

Although closely related to regular tiny brine shrimp, kids wouldn’t be fascinated by pets that they couldn’t see. So a lot of the work on adapting them focused on making them as large as possible.

Regular brine shrimp are significantly smaller than the half-inch expected length of the hybridized Sea-Monkey shrimp. That’s still very tiny, so many sea-monkey kits come equipped with magnifying glass viewing portals on the sides of the bowl to get a better view.

Unlike some pet fish, the expected size of sea monkeys is not limited by the bowl size that they are kept in, but they may show signs of stunted growth if they are not fed correctly or if the water temperature is too cold.

When using a Sea Monkey kit, the water preparation kit needs to be mixed with specific amounts of water. The ratio of salts to water is critical to ensure cysts hatch and continue to grow, so if you are using your own bowl to keep Sea Monkeys, ensure that mixing directions are carefully followed.

When you add a packet of Sea-Monkeys eggs to the brine solution, they seem to spring to life immediately. However, they are so tiny that they are hard to see when they first hatch.

To see newly hatched Sea Monkeys, it helps to put a flashlight against the bowl and gently stir the water. If your sea monkeys have hatched, you will observe tiny dots swimming against the current.

This immediate, almost magical, phenomenon is why they were first dubbed ‘Instant Life’ and only later became known as Sea-Monkeys. The eggs known as cysts that go into the brine resemble powder, but the shrimp grow quickly and are fully developed and ready to reproduce within four weeks.

Sea-monkeys molt up to seven times on the journey from a tiny spec of life to a fully grown adult. They have exoskeletons that become too small. The shrimp then breaks free from the tight shell and develops a new covering.

You may notice that your sea monkey is ready to molt as its color becomes slightly darker just before it breaks free from its restrictive outer shell.

Once Sea-Monkeys reach their full size of around half an inch, they can reproduce. Although the life span of an individual may only be a few months, it is easy to keep a colony alive for several years.

Here are some things that will affect the healthy growth of Sea-Monkeys:

  • Temperature of water
  • Food
  • Level of light
  • The concentration of brine in the water as a result of evaporation

Let’s look at each of these vital factors as they will significantly affect the growth of your Sea-Monkeys.

Water Temperature Affects the Growth of Sea Monkeys

Aquarium Thermometer Measuring Temperature

The temperature of the brine solution that the Sea-Monkeys are kept in will significantly affect their size. The growth of these small shrimp will slow down or may stop entirely if the water is too cold.

The best temperature to keep Sea Monkeys is in water at room temperature between 70 – 76F. The bowl should be placed where the temperature is relatively constant, so be careful not to position it on a hot window ledge or next to a heater.

Sea-Monkeys can adapt to slightly cooler climates, and colder water does not affect their lifespan. However, they are less likely to reach their maximum size of ½ an inch.

What to Feed Sea Monkeys for Maximum Growth

To keep your sea monkeys healthy and ensure that they grow properly, they must be fed correctly. However, it is dangerous for the entire colony to overfeed them, and more food does not equate to larger Sea-Monkeys.

For the first five days after Sea-Monkeys hatch, they must not be fed at all. They are able to live off the nutrients contained in their egg sacs.

Once you start feeding, only provide a minuscule amount of Sea-Monkey’ food’ every 5 to 7 days. Only increase the feeding amount if the number of tiny shrimp in your bowl becomes much larger than the initial group or there is no sediment on the bottom.

If the water becomes murky or dirty-looking, stop feeding your Sea-Monkeys immediately. Only resume when it looks clear and fresh again.

If you see a dark line running from the top to the bottom of your Sea-Monkeys, it means their guts are full, and they are eating well. There may also be a thin white line trailing from their bottoms which is healthy poop.

There are questions about whether or not special Sea-Monkey superfoods make these tiny crustaceans grow faster or larger, but it is fun to give it a try. Inexpensive special Sea-Monkey food supplements are available that claim to do everything from increasing growth rate to providing tasty treats.

To increase the growth of Sea-Monkeys and get more ‘big ones’ in your tank, you can try Sea-Monkey Gro-Kwikly, which promises notable growth within 48 hours, and Sea-Monkey Superfood, which makes similar claims. However, although Sea-Monkeys may occasionally slightly exceed ½ an inch in length, they will never start needing extra space in your home!

How Light Affects the Growth of Sea Monkeys

Closeup of a Phytolamp or Grow Light Illuminating Plants

Although it is not advisable to leave your bowl of Sea-Monkeys where the water can heat up excessively, these tiny creatures do seem to enjoy direct sunlight. This is because light also stimulates the growth of natural algae, which is an important food source.

Food is essential to ensure that Sea-Monkeys reach their maximum size, but it is pretty easy to kill them by overfeeding with the provided food sachet. Putting your Sea-Monkey tank in a high light position and not scrubbing off algae that forms on the glass is an excellent way to ensure that your Sea-Monkeys have a constant supply of available food without adding too much extra.

If you keep your Sea Monkeys in a low-light room, adding a plant grow light over the tank is a great way to stimulate the growth of algae and keep your sea monkeys happy. Sea monkeys do not need a night light.

How Water Evaporation Affects Sea Monkey Growth

Over time, water from the Sea Monkey tank may evaporate, affecting the brine concentration of the water. You may notice the tank’s water level decreasing or a chalky white layer of salts and minerals on the glass just above the waterline.

Do not be tempted to throw out all the water and replace it when you see that water is evaporating. Sea-monkeys can adapt to slow increases in brine concentration and will continue to grow and flourish.

If the water level drops significantly, you can add a small amount of room temperature distilled or bottled water, but do not add tap water which can contain purifiers that can kill the entire colony. If you need to replace a lot of water, you will need to get more sea monkey brine water solution and mix it as directed.

If you only add pure distilled water that does not contain the life-giving salts and minerals, the new water will dilute the brine solution. This may weaken the colony that needs the water to retain specific salt concentrations to grow well and remain healthy.

Are Males or Female Sea Monkeys Bigger?

When Sea-Monkeys first hatch, it is impossible to tell the males and females apart. The shrimp are all equally tiny with almost no discernable features, giving clues about how many of each sex you might have in a tank.

You don’t have to wait long though, and differences in the sexes start becoming noticeable from around three weeks. The males develop appendages under their chins that almost look like extra legs or little whiskers. They use these spare bits as arms that will assist in holding on to a willing female Sea-Monkey.

Female sea monkeys have smaller heads and feature a tiny egg-sac near the top of the tail. In general female Sea-Monkeys tend to reach larger sizes than males.

Females often exceed ½ inch and occasionally get closer to ¾ inch, while males seldom reach ½ an inch in length.

How Can I Make My Sea Monkeys Look Bigger?

Lit Portable Flashlight Laying on Floor

When you read some of the advertisements for Sea-Monkeys, you may feel really disappointed when you discover how tiny they are. One hardly knows what the fuss was about that made these little creatures a part of pop culture during the 60s and 70s.

You may not be able to get sea monkeys to grow very much larger no matter how perfect the conditions are, but there are a few things you can do to ensure that you can see them better.

The first thing is to get a special sea monkey tank. These nifty plastic tanks are usually included in Sea-Monkey setup kits and have special magnified sections. As the tiny brine shrimp flip past a magnifying glass, they will appear to instantly double in size and make them far easier to observe.

To view Sea-Monkeys inside your tank, it also helps to use a flashlight. These tiny creatures are attracted to light, so moving the flashlight around along the side of the tank will naturally make them flock towards the light.

Although it is fine to set up a light over the tank to make your Sea-Monkeys a feature, be sure the globe is not heating the water. Encouraging the sea monkeys to swim towards a light will definitely make your tank look more populated, and the Sea Monkeys will appear larger than they are.

You can also set your Sea-Monkey tank up so that it is closer to eye-level when you see them. Looking down on the tank will make them seem super small, but these energetic little creatures can become quite fascinating if you view them directly from the side, and they will appear larger.

One final trick to make your Sea-Monkeys appear bigger is to purchase special sea-monkey food that contains a red food additive. Take note – you cannot add regular dye to Sea-Monkey water as it will immediately kill them.

A specially formulated product called Red Magic can give your Sea-Monkey colony a boost of vitamins. In addition, it will add a red hue to their usual transparent bodies, which will make them a lot easier to see!

Final Thoughts

Sea Monkeys are hybridized brine shrimp that became popular 60 years ago, largely due to clever marketing. They are fascinating, no-fuss, instant pets that continue to be popular.

Although several advertisers claim that Sea-Monkeys can grow to outsize proportions, it is unlikely that even in optimal conditions, females will reach much more than ½ an inch in length, and males are slightly shorter.

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