Freshwater gobies and blennies are some of the more interesting and unusual species of aquarium fish. They originate from various habitats from all over the world. Some species can be more challenging to keep than others due to requirements of specific water parameters and live food, but they will reward a committed aquarist with interesting behaviours.
Water requirements
There are some very general guidelines for freshwater gobies and blennies below. However, the parameters for this group of fish can be wide ranging and very species-specific so it is important to check with your OATA retailer before purchasing.
- Salinity: Consult with your OATA retailer
- Temperature: between 24-27°C
- pH: 7.5-8.5
- Ammonia: Zero mg per litre
- Nitrite: Zero mg per litre
- Nitrate: Not to exceed 50 mg per litre
- General hardness: Medium-hard (8-18°dH)
- Carbonate hardness: Medium-hard (5-15°dH)
Biology
Gobies and blennies can be distinguished from each other through different features. Gobies will have their pelvic fins fused together into a ‘suction disk’. This is not present in blennies, who often have small hair-like growths near their eyes called ‘cirri’. Although termed ‘freshwater gobies and blennie’”, some of these species may require a very low salinity for long term care. Freshwater gobies and blennies will vary in size, with some such as the bumblebee goby (Brachygobius xanthomelas) only growing to about 2cm, whilst others, such as the freshwater blenny (Salaria fluviatilis), can grow up to 15cm. Freshwater gobies and blennies can be found in various habitats in the wild, including freshwater lakes, rivers and estuarine conditions.
Mixing freshwater gobies and blennies will depend on the species: some will require male and female pairs, whilst others will tolerate a male with several females or even mixed sex groups. Ask your OATA retailer for advice. Sexing freshwater gobies and blennies will vary by species: some will have very obvious differences, whilst others will be harder to sex unless breeding.
Aquarium requirements
As a general rule, you should within reason, buy an aquarium as large as possible. It is recommended that an aquarium of at least 40 litres is used for a group of the smallest species and at least 80 litres for a group of the larger species. The larger the aquarium, the more stable the environmental conditions such as temperature and water quality will be. Whatever the size, a filter is always essential.
The tank should also have aquarium fine gravel or sand to prevent injuries to their sensitive skin. Ideally, it should also be heavily planted with live plants to provide cover, especially if multiple males are being kept together. If live plants are not used, then the addition of plastic plants and suitable ornaments is recommended, such as wood, plant pots or model caves, which provides the fish with shelter. Freshwater gobies and blennies will require some area of cover to make them feel secure. Many species will also appreciate rounded pebbles and stones. An aquarium cover is essential as these fish can jump if startled. Some species will appreciate a faster flowing current than others, so always check with your OATA retailer for advice.
A heater is required to maintain a suitable temperature all year round. To minimise fluctuations in water temperature, the aquarium should not be situated near any draughts or heat sources. It should also be out of direct sunlight and away from loud noises, vibrations and sudden movements. Overhead tank lighting is recommended to maintain a correct day-night cycle.
Water testing kits are essential so that water quality can be checked on a regular basis (once a week) to ensure it does not slip below the water requirements stated earlier.
Introducing your fish
Before adding any fish, seek advice from your OATA retailer to make sure that your aquarium is an appropriate size for the number of freshwater gobies or blennies you would like to keep. Check that the water quality in your aquarium is suitable i.e. levels of ammonia and nitrite are zero. Only increase the number of fish you have in your aquarium slowly as the population of beneficial bacteria established when maturing your aquarium filter need to increase every time more fish are added and feeding increases. Overstocking or stocking your aquarium too quickly can result in ‘new tank syndrome’. This occurs when there are not enough nitrifying bacteria to cope with the increased waste from the fish, leading to unhealthy levels of ammonia and nitrite, which may cause fish to become ill or die.
Healthy fish have clear bright eyes, undamaged fins, intact scales, no ulcerations or bumps, appropriate swimming behaviour and steady breathing. Do not purchase a seemingly healthy fish if sickly fish are present in the tank with it. Signs of disease can include clamped fins, flicking against gravel or décor and shimmying (shaking). Diseases can be easily carried by fish that do not show any clinical signs. If in doubt, ask your OATA retailer for advice as they will have in-depth knowledge and experience.
Your OATA retailer will usually sell your fish to you in a plastic bag. Try not to keep them in this for too long. Once purchased, take your new fish home as quickly as possible because fish are easily stressed by bright lights, extreme temperatures, noise and movement.
Once home, your fish will need to acclimatise to their new environment and a common method of doing this is known as the ‘floating bag’ method. Switch off the aquarium lights and take the bag containing your new fish out of its outer wrappings carefully, avoiding exposure to bright light. Float the bag in the water of your tank to ensure the temperature in the bag is the same as the aquarium water. After 10 minutes, slowly introduce small amounts of aquarium water into the bag containing the fish for up to 20 minutes. Once complete, carefully release the fish into the aquarium whilst introducing as little bag water into the aquarium as possible. After this, dispose of the bag and any excess water appropriately. Monitor your new fish carefully for the first week, paying particular attention to water quality. If in doubt, contact your OATA retailer for advice.
Maintenance
At least once every week, a partial water change of 25% is strongly recommended (a siphon device is useful to remove solid waste from the gravel). The water should be tested regularly (at least once per week) to ensure that ammonia and nitrites don’t build up. Ensure that the replacement water is treated with tap water conditioner to remove any harmful chlorine or chloramine present before adding to the aquarium.
Filters should be checked for blockages. If the filter needs cleaning, do not run it under the tap because any chlorine or chloramine present may kill the beneficial bacterial population that has established in the media. Instead, it should be rinsed lightly in the tank water which is removed during a partial water change as this reduces the amount of bacteria which are lost.
Good husbandry is essential as freshwater gobies and blennies can be stressed by even the smallest amounts of ammonia and nitrite which may then cause them to develop various diseases. Test the water to monitor the ammonia, nitrite and nitrate levels, together with pH and water hardness every week, especially during initial set-up and after adding extra fish.
What to watch out for
All fish will have slight variations in their behaviour or appearance, but keeping an eye on any changes in the following will help to identify any potential problems before they become a real health issue:
- swimming behaviour – hanging at the surface, sitting on the bottom or erratic swimming
- colour – turning a darker or paler colour than normal
- temperament – changes in level of aggression or hiding more than normal
- breathing – gill covers moving at a slower or faster rate than normal
- appearance – development of white spots or fluffy growths, loss of fins or scales
- condition – increase or decrease in body weight and condition
- feeding – reduced intake or lack of interest in food
If you are concerned about the health of any of your livestock, then test your water quality and contact your OATA retailer for further guidance.
Feeding
Generally freshwater gobies and blennies are omnivorous. Small meaty frozen items such as daphnia, plankton and brine shrimp are good staples, however some may need feeding live food before they adapt to frozen food. In time, they may learn to take sinking pellets or flakes, which will help to vary their diet. Some may graze on algae and biofilms which will need to be substituted with pellets, if there is insufficient in the tank.
Freshwater gobies and blennies should only be fed what they can eat within a few minutes, once a day. Take care not to overfeed as this can lead to a build-up of uneaten food which breaks down releasing toxic waste into the water. If in doubt, ask your OATA retailer for advice on appropriate feeding levels.
Compatibility
As freshwater gobies and blennies are from such specific habitats, they should only be mixed with other species which can tolerate the same conditions. Few are well-suited to a standard community aquarium. Always ask your OATA retailer before mixing freshwater gobies and blennies with other species.
Breeding
Success in breeding freshwater gobies and blennies will vary depending on the species. Although some species may breed in home aquariums, it is unlikely the fry will survive as in the wild they will be washed out to sea as part of their natural life-cycle, a process which would need to be replicated in aquariums. However, there are records of bumblebee gobies being bred successfully in captivity. The female will deposit eggs in a cave which the male will then guard. When the fry hatch, which will depend on temperature, they will require baby brine shrimp for food. A specialised set-up is required for best results.
Checklist
Before purchase make sure:
- You have the appropriate equipment and position for the aquarium.
- You have researched all the species in which you are interested and your final choices are all compatible.
- You are familiar with how to transport and release your fish.
- You are aware of the daily, weekly and monthly maintenance your aquarium will require.
- You are prepared to look after your fish properly for the duration of their life.
Shopping list
- Glass or acrylic aquarium
- Filter*
- Heater
- Lighting (required for live plants)*
- Gravel or sand
- Tap water conditioner/dechlorinator
- Gravel cleaner/siphon cleaning device (recommended)
- Water testing kits (ideally ammonia, nitrite, nitrate, pH and water hardness)
- Aquarium decorations and/or live plants
- Bucket for water changes
*may be included in branded aquarium sets but can be purchased separately.
Before purchase make sure:
- The aquarium is of a suitable size that ideally can accommodate the fish once they are fully grown.
- Water parameters are as advised in this leaflet.
- Aquarium is cycled and ready to receive fish.
Top tips
Always buy…
test kits and regularly check the water for ammonia, nitrite, nitrate and pH. This will allow you to make sure the water in your aquarium is not causing welfare problems for your fish.
Establish a routine…
for testing the water in your aquarium. Record your results to enable you to identify fluctuations quickly. Also check the temperature of the water.
Maintain…
the water in the aquarium within the accepted parameters highlighted above. You may need to do regular water changes to achieve this.
Always wash your hands…
making sure to rinse off all soap residues, before putting them into your aquarium, or use long sleeved rubber gloves. Wash your hands again afterwards and certainly before eating, drinking or smoking.
Never siphon by mouth…
A fish tank can harbour bacteria which can be harmful if swallowed. Buy a specially designed aquarium gravel cleaner which can be started or primed without the need to place the siphon in your mouth.
Five Welfare Needs Checklist:
The Animal Welfare Act 2006 states that all pet owners have a legal duty of care to their pets. Anyone who is cruel to an animal or is found not to be providing the five animal welfare needs, as listed below, can be prosecuted.
- A suitable environment e.g. appropriately sized tank (with water heater if tropical set up) within a suitable location in your home.
- A suitable diet which meets the needs of your chosen fish.
- Behaviour – Fish are able to exhibit their normal behaviour e.g. hiding places for timid fish, enough room for fish to swim freely.
- Companionship – Ensure you know whether your chosen fish need to be kept with, or apart from, other fish.
- Health – Protected from pain, injury, suffering & disease e.g. you are aware of the daily, weekly and monthly maintenance that your aquarium will need.
Remember...
Water quality test kits are a necessity not an optional extra.
You must be prepared to look after your fish properly for the duration of their life and provide an aquarium which can accommodate your fish when fully grown.
Never release your aquarium animals or plants into the wild. It is illegal and for most fish species this will lead to an untimely and possibly lingering death. Any animals or plants that do survive might be harmful to our native countryside. Take care to properly dispose of any soiled substrate (e.g. sand or gravel) water or decorations so that non-native organisms do not enter natural watercourses.
