Art by Alexander Vasiljev, Copyright © 2017


Thursday, September 21, 2017


read introduction here

Ranchu are omnivores and prefer a wide variety of foods. To insure health and reduce obesity, their diet has to be balanced with proteins, carbohydrates, minerals and vitamins.

Foods high in protein:
  • live or frozen brine shrimp
  • daphnia
  • bloodworm
  • pellets

Foods high in vitamins and minerals:
  • algae
  • duckweed
  • chlorella and phytoplankton
  • spirulina
  • pumpkin
  • spinach
  • wolffia

Food Types And Digestion Times

Food with less moisture content takes longer to digest. A safe interval between feedings can be placed at 2 hours, however digestion time will change depending on the amount of food given. Approximate digestion times:
  • daphnia, brine shrimp, wolffia, duckweed - 1 hr
  • bloodworm - 1 ½ hr
  • pellets - 2 hrs. 


One of the foods that is central to ranchu development. Easily digestible and highly absorbent, daphnia is high in nutrients and contributes to a maximum fry growth potentials.


Another food that is very important to ranchu. It has superior digestion and absorption rate. High in protein, it promotes head-growth and overall development.

Brine Shrimp

With excellent absorption rate and nutritional value it is a good alternative to daphnia. Newly hatched brine shrimp is excellent for feeding fry.


Low in fat and protein, vegetables are rich in vitamins, minerals and organic pigments, and are very important supplement. They promote colors and overall health, especially at young stages. Most used vegetables are: phytoplankton, green algae, chlorerlla, spirulina, duckweed, pumpkin, wolffia and spinach among others.

Commercial Pellets

Due to low moisture content, digestion rate is the slowest, up to 2 hrs and more. Best if pellets are alternated with easily digestible foods, e.g. bloodworm. Due to high nutritional value and longer digestion times, feeding only with pellets may cause obesity and requires carful observation. There are many brands that offer ranchu pellets. However, not all of them are equal in quality and value. My own preference is Azayaka Brand ranchu pellets. Here is my article on different brands of pellets, their comparison and analyzes.


Organic pigments or carotenoids like luteins (for yellows) and astaxanthin (for reds) are very important for developing fish coloration. Incorporating spinach, pumpkin, duckweed, wolffia and color enhancing pellets is beneficial.


Wolffia is the world’s smallest flowering plant that belongs to a group of duckweeds. It is easily digestible, contributes to color development (especially yellow) and overall health of a young fish. It also helps to maintain a slim belly. Wolffia can be easily substituted with duckweed.

Benefits of Wolffia or Duckweed:
  • promotes head-growth development
  • promotes slim belly and good physical shape
  • easily digestible
  • rich in vitamins and minerals
  • high in protein
  • positively effects color development
  • shades the water and helps to lower water temperature
  • removes access of oxygen and supplies carbon dioxide
  • utilizes ammonia 

Cultivating Wolffia or Duckweed:
  • requires a lot of sunlight
  • tap water can be used
  • provide light aeration
  • will propagate very rapidly in 86 F (30°C)
  • keep water temperature under 97 F (36°C)
  • in winter, if temperatures are low, will go dormant and will sink to the bottom

Tuesday, September 19, 2017


read introduction here

Concrete Pond

Concrete has been a long time favorite material for building traditional ranchu ponds. Common sizes are 6.6 ft x 6.6 ft x 10in (2m x 2m x 25cm) and 5ft x 5ft x 10in (1.5m x 1.5m x 25cm). Square size is easy to arrange in succession, maintain and clean.

In the past, there was an indentation made on the bottom of the pond in the shape of a square, for collecting and removing of debris and for the fish to be kept during the water change. Also, there was a white tile placed on the bottom of the pond to determine translucency and color of the green water. However, nowadays, these features are not used.

Fiberglass or Polyethylene Pond

These materials are strong and durable and are commonly used in modern days and have good qualities for thermal insulation. Although, if the walls are too thin the pond might get deformed under the water weight.

Plastic Pond 

Any large plastic container, e.g. cement mixing tub or children’s pool, etc, can be used, as long as it's depth is between 9-12in (22 - 30cm). These containers are durable, cheap and come in different sizes, shapes and colors. Quite suitable for raising fry and young ranchu.

Pond Liner

It is a good option for DIY and can be used to create pond of any size and shape. Although, it is more prone to leaks.

Sunday, September 17, 2017


read introduction here


It is necessary to have at least 3 hours of sunlight a day. Sunlight is very important for a healthy ranchu and aids in brighter colors and it is instrumental for photosynthesizing phytoplankton and wall algae growth, sustaining healthy environment. As a positive side effect, sunlight's ultraviolet rays are anti-bactericidal. Watch for ranchu getting too stimulated by sunlight, as excessive swimming may weaken their tail tension, especially when young.


Strong direct sunlight can cause deterioration of ranchu physical condition and with water depth of only 6-10 in (15-25 cm) the pond can get easily overheated. It is important to shade the pond if water temperature rises near or above 86 F (30°C). However, avoid excessive shading, as it reduces the sense of seasons in ranchu.

Cheese cloth, synthetic shade cloth or bamboo/reed blinds can be used to shade the pond. It is suggested to position shading material 6.6 ft (2 m) above the water surface to provide sufficient ventilation and gas exchange.

Friday, September 15, 2017


read introduction here

Adequate aeration is important in supplying water with oxygen. It also aids in better water circulation and equalizes temperature between different layers in the pond. 

However, vigorous aeration can have a negative impact on developing ranchu, especially their tale formation. It is very important to bring aeration to its minimum or avoid it all together during eggs hatching and fry development and, when the tail starts to form and open.

Advantages of aeration:
  • supply of oxygen to the water 
  • release of carbon dioxide from the water 
  • mixes water for more uniform water temperature 
  • delays deterioration of the water quality 

Drawbacks of aeration:
  • too much aeration loosens the tail tension and effects its shape 

Oxygenation And Water Surface 

Pond surface is important for oxygenation. If covering or shading the pond, attention should be paid not to obstruct the airflow and gas exchange. It is necessary to provide good ventilation if the pond is inside or when air temperatures are high.

The Amount of Dissolved Oxygen And Water Temperature

There are two factors that effect how much oxygen is dissolved in the water: temperature and pressure.

With shallow pond used for ranchu, water pressure does not have much effect. The amount of dissolved oxygen will primarily depend on increase or decrease in temperature. As a rule, with temperature increase the amount of dissolved oxygen will proportionally decrease:

  • 32 F (0°C) - 14.16 ml/L 
  • 34 F (1°C) - 13.77 ml/L 
  • 41 F (5°C) - 12.37 ml/L 
  • 50 F (10°C) - 10.92 ml/L 
  • 59 F (15°C) - 9.76 ml/L 
  • 64 F (18°C) - 9.18 ml/L 
  • 68 F (20°C) - 8.84 ml/L 
  • 77 F (25°C) - 8.11 ml/L 
  • 86 F (30°C) - 7.53 ml/L 

In the summer, due to higher temperatures water oxygen levels are at their lowest. Ranchu requires more oxygen in the summer, as it is most active. If there is a lack of oxygen in the water, ranchu will be swimming “nose up” at the surface gasping for air. Sufficient aeration is required, as well as the appropriate stocking density.

Oxygenation And Green Water

Phytoplankton in green water photosynthesizes and supplies oxygen to the water. When water gets over saturated with dissolved oxygen, it starts to escape in the form of gas. So called “gas bubble disease” may occur, when oxygen gas bubbles appear in the fish bloodstream and become visible on gills, fins and eyes. It can cause a secondary infection or even be fatal.

When using green water, additional aeration may not be necessary. Still, keep an eye on oxygen level becoming too low.

Monday, September 4, 2017


read introduction here

Ranchu Body Temperature

Ranchu are ectothermic animals, which means their body temperature matches the temperature of the environment. They are also eurythermal, meaning that they are able to tolerate a wide range of temperatures. Depending on the environmental conditions, ranchu will adjust their metabolism.

Optimal temperature for ranchu active growth is between 64-86 F (18-30°C). As the water temperature rises above 86 F (30 C), ranchu activity becomes suppressed, negatively impacting their development. When the temperature drops below 64 F (18 C), ranch's metabolism begin to slow down. Below 43 F (6 C), ranchu enter a hibernation state. Cold temperatures, however, are part of ranchu's natural life cycle and are beneficial. As a temperate climate fish, ranchu enjoy all four seasons.

Temperature Fluctuations

Ranchu is adaptable to a wide temperature range, but only if the temperature changes gradually. It is best if the temperature increases no more then 1.8 F (1°C) degrees per day. A sudden increase of 9 F (5°C) degrees can be lethal, especially for fry and young fish. In an emergency, if the water temperature must be increased quickly, for disease treatment, it has to be done in increments of no more than 4-5 F (2-3°C) degrees per day until the desired temperature is reached. Decreasing the temperature is much better tolerated by the fish, but a gradual change is best.

It is important that the water temperature difference between early morning and noon fluctuates no more than 18 F (10 C) degrees. If it exceeds that - shading, ventilation or a bigger container is required.

Ranchu Activity & Water Temperature 

The range of water temperatures suitable for ranchu is between 30 and 100 F (-1 to +38°C). However, each temperature level dramatically effects the fish's physiology:
  • 32-43 F (0-6°C) - full hibernation state, ranchu are inactive
  • 44-54 F (7-12°C) - semi-hibernation, physiological functions are slow
  • 55-64 F (13-18°C) - intermediate state between hibernation and active state; physiological functions are not up to their fullest 
  • 65-75 F (19-24°C) - fish is ready to spawn, gonads develop; pathogens become more active 
  • 76-86 F (25-30°C) - active fish growth 
  • 87-97 F (31-36°C) - fish growth supressed 
  • 98-100 F (37-38°C) - upper water temperature limit for ranchu 
  • above 100 F (38°C) - temperature is NOT suitable for ranchu 

Use of Heater 

Although, a heater isn't necessary for day-to-day ranchu keeping, it might be useful in some situations. For the most part, breeders use it to adjust spawning time, to incubate ranchu eggs and to control the beginning stages of ranchu fry. A heater can also be used to aid in treating some diseases.

  • setting water temperature as desired 
  • controlling to big of a temperature fluctuation during the day 
  • to interrupt hibernation 
  • adjusting spawning season 
  • adjusting hatching date and promote fry growth 
  • increase disease treatment outcome 

  • difficult to keep the same water temperature during water changes 
  • lack of four season temperatures may lead to obesity 
  • temperatures that are kept the same, lead to more rapid water quality deterioration 
  • electrical bill