Expanded Fish Care

Medaka Japanese Rice Fish

Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Beloniformes

Family: Adrianichthyidae

Genus: Oryzias

Species: Oryzias latipes

Care level- Easy-Experienced  

Temperament and Behavior- Peaceful.

I keep Blue Daisy and Pearl Galaxy Rice Fish, and both are peaceful, beautiful fish. However, I find the Blue Daisy Rice Fish are shyer compared to the Pearl Galaxy Rice Fish. The Blue Daisies are more likely to cluster together and hide where the Pearl Galaxy is often out swimming independently of each other. 

Lifespan- 1-4 years 

Size- up to 1.5 inches 

Diet- Omnivores. I have fed the Rice Fish all kinds of food, from flakes to tiny insects that rest on the floating algae in the outside tubs. If you push down slightly on the algae it allows for a small amount of these almost microscopic bugs into the water. In that case, the Rice Fish go crazy eating. I do keep most of my Rice Fish outside in a smaller-sized tub. They enjoy insects, larvae, and krill flakes. 

Minimum Tank Size- I would recommend nothing less than 10-gallon. However, the Blue Daisy Rice Fish in my fish room has done well in a 20-Long aquarium. From my experience, Rice Fish I keep do pick around in the substrate from time to time; however, they spend the most time towards the surface. If you can, I would recommend the footprint of the 20-Long aquarium, an aquarium with more swimming length vs. swimming depth.  

pH-7.0-8.0

Water Hardness- Hard Water 

Temperature- 62-80 degrees Fahrenheit- The perk about keeping Rice Fish is that you don't need to worry about temperature as much as other fish species. These Fish do exceptionally well in a non-heated aquarium. I currently keep Rice Fish inside an aquarium and outside in a tub. Each environment does well, but these Rice Fish setups are entirely different. No matter how you choose your Rice Fish, inside or outside the best thing you can do is keep the environment as consistent, as possible.

Tank-mates- I have only kept Rice Fish with Neocaridina Shrimp. However, a peaceful, smaller fish species that are suited for cooler water temperatures could be a possibility for a tank-mate. White Cloud Minnows or Rosy Red Minnows are fish species that enjoy similar water parameters.  

Recommended Group Size- This species does better in a group, no less than 4-5. 

Tank Set-up-I kept Blue Daisy Rice Fish in both a 20-Long aquarium and outside and they have bred and done well. I keep the Pearl Galaxy Rice fish in an outside 30-gallon tub. Over a couple of years of keeping Rice Fish, there is no comparing how much more fry (offspring) I have yielded outside in the tubs vs. inside. The Pearl Galaxy Rice Fish tub outside has a mix of pea gravel and play sand for the substrate. In the beginning, I did have an air stone that I could dial down the airflow with a valve. This species enjoys calm, gentle water flow, found naturally in shallow rice field paddies. The Blue Daisy Rice Fish are in a 20-gallon-long aquarium. The substrate is a mix of Fluval Stratram with a few plants. Something that has worked for me in breeding this fantastic fish. Is to provide the females a place to scatter their eggs. Outside, the tubs have many floating plants, not many rooted aquarium plants. The female's eggs are sticky, and as they swim through the flowing plants, she will sprinkle her eggs around, sticking to plants and plant roots. 

I provided more planted aquarium plants in substrate vs. floating aquarium plants for the inside Blue Daisy Rice Fish. It was not till a large area of hair algae began to grow that I started to see eggs on the females. I had removed all algae in the past. However, I recently allowed a small bit of Hair Algae to grow and take over a corner of the aquarium. Once this grew in, I began seeing females scattering eggs and a fry swimming around. I always continued water changing, not removing the Hair Algae, and occasionally trimming. I just allowed an area of algae to continue to grow, only clipping back when it was starting to take over. The hair algae can be an eyesore; however, it serves as a safe place for females to scatter their eggs. Again, I did see breeding both inside and outside; however, they do considerably better out in the tubs. 

Males v. Females  When I first started keeping Rice Fish, it was challenging to tell the difference between males and females. A few years later, it's still not easy to tell the males from the females at a glance. The appearance between the two is similar, and the only sure-fire way to know if you have a female is to see her carrying eggs. However, the males are usually smaller and have slender bodies.

In contrast, females are generally larger and rounder in body stature. If you are looking at the fins of your Rice Fish, males will have a more pronounced anal fin, and this fin is located towards the tail fin but on the underside belly region.  

Breeding- Rice Fish are not difficult to breed, and if you provide the right environment, you could easily see fry. Even though Rice Fish look like Guppy fish, they are not livebearing fish. However, they do have the capability to produce fry just as often as livebearers.

When it comes to breeding Rice Fish, I have had a significant difference between keeping them outside in a tub versus keeping them in an aquarium inside the fish room. Both have bred; however, keeping them outside yielded too many fry to count. Inside only a handful survived to adulthood. A few factors affected why I see more Rice Fish fry outdoors, food availability is a large part. Having a plethora of microscopic food in the water column with an equal amount of bug larva and tiny water critters for the adults and fry can always eat. No doubt a contributing factor to the survival rate of the fry in the backyard tubs. 

Breeding happens most in the warmer months and most often in the morning. Once the females have fertilized eggs, you will see a grape-like cluster on the underside, belly region by the anal fin. You will see the female swimming and sticking eggs to floating vegetation. I see another batch of fry every two weeks in the summer when the weather turns into the fall months, I do not typically see fry in the outdoor tub. Rice Fish Fry is extremely small once hatched. I will scoop them out into a separate outdoor tub to grow out upon discovery. I do not see the adults eating eggs; however, they will eat their fry. For the best results, I will rotate the floating plants or spawning mop that are with the adult Rice Fish and transfer them to the fry-only grow-out tub. If I see eggs stuck, I will move the plants and spawning mops to the grow-out tub for approximately two weeks then I will move them back to the adult tubs.

For the inside Rice Fish, I have had breeding success, but nowhere to the success of the outdoor tubs.

Fry- Once the adult female scatters their eggs, the eggs only take short time to hatch. You will see an extremely small fry, barely the size of a grain of rice. Adults will give no care and are often eaten by larger Rice Fish. Fry will stay toward the surface staying close to the floating plants for safety and protection. The benefit to caring for Rice Fish outside is the added benefit of all the live microscopic food.