Before You Start Keeping Octopuses
Octopuses are cephalopods (members of the phylum Mollusca), not vertebrates, and have completely different life processes from common fish. Because of their high intelligence, color-changing abilities, and the dexterity of their suckers, they are popular exhibit animals in aquariums. However, keeping them in home aquariums is quite difficult and requires special attention.
Main species kept in Japanese households:
- Japanese Common Octopus (Octopus vulgaris): Widely distributed along Japanese coasts. Most readily available.
- Cuttlefish (Sepia): Strictly speaking, cuttlefish (not actually octopuses, but fellow cephalopods). Moderately difficult to keep.
- Lesser Octopus (O. minor): Small octopus. Relatively easy to handle.
The Most Critical Concern: Escape
Octopuses have an exceptionally high ability to escape from aquariums. Because they lack a skeleton, they can escape through even small gaps (3-4 cm).
- A completely sealed lid is essential: Use a glass or acrylic lid that can be weighted down or secured firmly in place.
- Close gaps in pipes and tubing: Octopuses may attempt to escape through gaps in pump hoses or around live rocks.
- Make checking the tank a routine: Verify the lid's condition daily.
Death from dehydration after escape is the most common accident. If you cannot implement these measures, we do not recommend keeping octopuses.
Equipment Needed
Tank Size
| Type | Minimum Recommended Size |
|---|
| Lesser Octopus / Small species (15-20 cm) | 60 cm (75L or larger) |
| Japanese Common Octopus (20-30 cm adults) | 90-120 cm (150L or larger) |
| Large species (over 30 cm) | 120 cm or larger (200L+) |
Because octopuses have a wide range of activity, it is ideal to provide the largest tank possible.
Water Quality Management
Octopuses are more sensitive to water quality changes than fish, and the following parameters are especially important to manage.
| Parameter | Recommended Value |
|---|
| Water temperature | 20-24°C (Japanese Common Octopus) |
| Specific gravity | 1.023-1.026 |
| pH | 8.1-8.3 |
| Ammonia / Nitrite | Undetectable (0) |
| Nitrate | 20 ppm or below |
Water temperature management is especially critical. Japanese Common Octopuses are temperate species and cannot tolerate high water temperatures (above 26°C), so a chiller may be necessary during summer.
Filtration Equipment
Octopuses produce large amounts of waste, ink, and uneaten food. Powerful filtration is essential.
- Protein skimmer: Extremely effective for removing organic matter. Almost essential in octopus tanks.
- External filter (flow rate 2-3 times the tank volume)
- Activated carbon filter: Effective for water quality recovery after ink release.
Setting Up Hiding Spots
Octopuses require hiding spots (caves or hole-like spaces).
- Caves made of stacked live rock
- Unglazed clay pipes or octopus pots (approximately 15-20 cm in height and width)
- PVC pipes
Without hiding spots, octopuses experience chronic stress and may die prematurely.
Feeding and Diet
Octopuses are carnivorous and eat crustaceans, mollusks, fish, and other animals.
Main Foods
| Food | Characteristics |
|---|
| Live food (small crabs, shrimp) | Most preferred. Stimulates hunting instinct and encourages active behavior. |
| Frozen shrimp (whiteleg shrimp, spiny lobster) | Easy to obtain and can be stored. Thaw before feeding. |
| Frozen clams and scallops | Feed with shells open. |
| Frozen fish (mackerel, sardine pieces) | Can be used as a supplement. |
Feeding frequency: Once daily as the standard (adults can be fed once every 2-3 days). Always remove uneaten food (a major cause of water quality deterioration).
After an octopus releases a large amount of ink, quickly recover water quality by performing a water change and replacing the activated carbon filter.
About Tank Mates
Octopuses should fundamentally be kept alone.
- They will likely predate on other fish and crustaceans.
- Keeping multiple octopuses together carries the risk of cannibalism.
- Other invertebrates such as anemones will also be preyed upon.
We strongly recommend keeping octopuses alone in a dedicated tank where they are the main attraction.
Octopus Intelligence and Environmental Enrichment
Octopuses are considered to have the highest intelligence among mollusks, and they display problem-solving, play, and distinctive behaviors. In captivity, boredom and monotonous environments cause stress.
- Provide toys: Small balls, bottles with lids (with food inside).
- Vary where you hide food: Octopuses tend to lose interest if food is always in the same location.
- Change the layout: Periodically rearrange the live rock placement.
Through these enrichment activities, octopuses can maintain more active and healthier conditions.
Octopus Lifespan and Reproduction
Octopus lifespan varies greatly by species, but the Japanese Common Octopus has a relatively short lifespan of about 1-2 years.
- Death after egg-laying: Female octopuses stop eating and die while guarding their eggs after laying (a behavior common to all cephalopods).
- Breeding: Reproduction in tanks is possible, but raising larvae is extremely difficult (they require planktonic food).
Legal Considerations
If you are keeping an octopus collected domestically, check your local and prefectural fishing regulations. In some areas, permission may be required for collection and keeping. If purchasing, obtain your octopus legally from an aquarium or marine fish specialty store.
Summary
Keeping octopuses presents unique challenges in escape prevention, water quality management, and solitary housing. However, their intelligence, color-changing abilities, and distinctive behaviors make them a rewarding species to keep. With a completely sealed lid, powerful filtration, a protein skimmer, and proper temperature control in place, you can enjoy a fulfilling life with a highly individualistic octopus. We recommend beginners start with small species like the lesser octopus.
