Cochus Blue Tetra (Boehlkea fredcochui) – 2–4cm+ Size Grades

Meet the Cochus Blue Tetra

Cochus Blue Tetra is the trade name used here for Boehlkea fredcochui, a freshwater characin from South America. A natural-history summary of Cochu’s blue tetra places its range in the Amazon Basin and notes that it is commonly kept in aquariums. That geographical background describes the animal’s natural history rather than setting aquarium water targets.

FishBase records Boehlkea fredcochui in the family Stevardiidae, with a benthopelagic freshwater environment and a maximum of 5.4 cm total length for male or unsexed fish. The maximum is the decisive size for planning space: it is not an average, but it gives a sensible upper figure around which to arrange the aquarium and screen possible companions. FishBase also assesses the species as Least Concern.

Decide whether its social needs fit your aquarium

This is a shoaling tetra rather than a fish to plan around as a single specimen. It suits a keeper who can maintain a properly filtered aquarium, reserve open swimming space, keep a same-species group and follow a weekly water-care routine. The important decision is therefore not simply whether one small fish fits: it is whether the aquarium can support the whole intended group at adult size alongside every other resident.

For comparisons with other members of this familiar aquarium group, browse our current tetras collection. Compare adult size, water needs, social requirements and temperament independently rather than treating every tetra as interchangeable.

The gallery images are representative of this type of animal rather than photographs of the exact animal supplied, so colours can look slightly different from the live animal.

Choose the dispatch size and quantity separately

One purchase quantity supplies one animal of the selected option. The dispatch-size options are 2 cm, 3 cm and >4 cm; use the live size selector to see which option can be chosen. The greater-than sign on the >4 cm grade means that animal is dispatched above 4 cm rather than at an exact 4 cm measurement.

The size you select is the size supplied, not the adult size.

Dispatch grade and social quantity answer different questions. The grade describes the approximate size of each animal when sent, while the quantity controls how many animals are purchased. For example, selecting the 3 cm option with a quantity of five means five individual animals from that dispatch grade. It does not mean one group hidden inside a single purchase unit.

Plan from 5.4 cm, not from the dispatch measurement

A 2 cm or 3 cm animal still needs an aquarium chosen around the FishBase maximum of 5.4 cm total length and the intended shoal. A larger dispatch grade does not change that adult planning figure, the need for filtration or the social minimum. It only changes the size at which the animal enters the aquarium.

Sex is guaranteed only when the selected option explicitly states male or female. This Cochus Blue Tetra listing has no sex-guaranteed option.

Review the current delivery and Live Arrival Guarantee policy before arranging receipt. Use the live selector for size choice rather than relying on a static description of option status.

Plan around the decisive care numbers

OATA’s freshwater tetra guidance gives 22–27°C, pH 6.5–8.0 and 4–12°dH as group-level aquarium guidance rather than a species-specific optimum. FishBase separately records the species in environments of 22–26°C, pH 6.0–8.0 and 5–12°dH. These ranges overlap substantially, allowing an aquarium to be planned without pushing towards an outer limit.

Because the recorded maximum passes the 5 cm threshold used in OATA’s aquarium guidance, use at least 80 litres as the starting planning reference for a small shoal. Larger aquariums make temperature and water quality more stable, but volume alone is not enough: the layout must still provide shelter, usable swimming space and capacity for all other residents.

Apply the social number to this tetra itself. Five is the stated minimum, while a larger group may be chosen where the aquarium’s volume, filtration and total stocking allow it. Keeping one or too small a group may cause stress, so decide the intended quantity before choosing the remaining community.

Check whether this animal suits the aquarium

Mature the filter before adding the shoal

A working biological filter is essential. The RSPCA explains aquarium filtration as a biological process: fish release toxic ammonia, beneficial bacteria convert it to toxic nitrite, and further bacteria convert nitrite to the safer nitrate. A filter therefore needs to be established and maintained as a living biological system, not treated merely as a device that moves water.

Prepare and mature the aquarium before the fish arrive. Our guide to setting up a first tropical tank provides a practical route through that preparation. Test the finished aquarium and add fish only when ammonia and nitrite are both zero mg per litre.

Use test results to make the stocking decision

Every additional fish and every increase in feeding adds waste that the bacterial population must process. Increase the aquarium population slowly so those bacteria can expand with the load. Adding too many animals too quickly can lead to new tank syndrome, in which ammonia or nitrite rises because the biological filter cannot process the new waste.

Choose filtration for the whole aquarium rather than for one small dispatch-grade fish. The system must support at least five Cochus Blue Tetras at their adult planning size, plus all other inhabitants and the food entering the tank. A large nominal volume cannot compensate for an immature, blocked or poorly maintained filter.

Balance cover with open swimming space

Use aquarium gravel or sand as the substrate and provide shelter with live plants where practical. If live planting is not part of the design, use aquarium-safe artificial plants and suitable ornaments such as model caves or plant pots. Cover gives fish somewhere to withdraw, while the remaining open area lets the group move without every route being obstructed.

Divide the layout by function

A useful layout does not force a choice between a densely furnished aquarium and a completely bare one. Group plants and ornaments so they create distinct refuge areas, then retain a continuous open route through the aquarium. Check the arrangement from the fish’s point of view: decoration should not divide the swimming space into narrow dead ends or prevent access to shelter.

OATA includes a gentle current in its advice for smaller tetras. Arrange the filter return so filtration remains effective while fish can use both open and sheltered areas. Watch their normal swimming rather than assuming a visually impressive flow is suitable. Persistent hanging at the surface, sitting on the bottom or erratic swimming belongs in the health-check routine and should prompt an immediate water-quality check.

The 80-litre planning baseline is only the beginning of the space decision. Consider the shape and usable interior after substrate, plants, ornaments and equipment are installed. A larger aquarium generally offers more stable temperature and water quality, yet it must still be arranged so the group has both cover and room to move.

Match the water before adjusting the aquarium

Start by measuring the aquarium rather than choosing values by guesswork. Use our aquarium water chemistry guide to understand temperature, pH, hardness and nitrogen readings, then compare the measurements with this animal through the water matcher.

Read the two ranges for their intended purposes

For a straightforward planning window shared by both sets of figures, 22–26°C, pH 6.5–8.0 and 5–12°dH sit within their overlap. Measure prospective tank mates against the same aquarium values; two fish being described as tropical does not by itself mean their full water requirements match.

Keep ammonia and nitrite at zero mg per litre. OATA places nitrate at no more than 20 mg per litre above the normal tap-water level, so the tap reading matters. If tap water measures 15 mg per litre nitrate, the corresponding upper aquarium figure is 35 mg per litre. This is an upper limit rather than a target to aim for.

General hardness and carbonate hardness answer different questions. The OATA aquarium figures are 4–12°dH general hardness and 3–10°dKH carbonate hardness. Record both where the test method distinguishes them. A pH result without the hardness context gives only part of the picture, particularly when comparing the aquarium with another species’ requirements.

Take action from the complete set of measurements. A temperature inside range does not cancel out detectable ammonia, and a suitable pH does not make an overcrowded or immature aquarium safe. Confirm the values together before introduction and continue testing after the population or feeding level changes.

Use a repeatable weekly maintenance routine

Carry out a 25% partial water change at least once every week. Use a siphon to remove solid waste from the substrate while water is withdrawn, and treat replacement tap water with a suitable conditioner before it enters the aquarium. Conditioner is necessary because chlorine or chloramine can harm the biological filter.

Turn the percentage into a measured task rather than estimating it by eye. If the aquarium contains 80 litres of actual water, 25% is 20 litres. Where substrate, decoration or an unfilled top section reduces the true water volume, base the calculation on the water present rather than the aquarium’s headline capacity.

Complete the jobs in a consistent order

1. Test ammonia, nitrite and nitrate, recording the readings so changes are visible.
2. Siphon 25% of the aquarium water while removing waste from accessible substrate.
3. Prepare replacement water and treat it for chlorine or chloramine.
4. Check the filter intake, outlet and media for reduced flow or blockages.
5. Rinse media lightly in the removed aquarium water when cleaning is needed. Do not run it under the tap.
6. Return the filter to normal operation and confirm that water is moving through it.

Do not run the filter media under the tap. Chlorine or chloramine may kill the beneficial bacterial population that processes ammonia and nitrite. Light rinsing in water removed during the partial change reduces the amount of bacteria lost while clearing material that restricts flow.

Test at least weekly even when the aquarium looks clean. Clear water can still contain ammonia, nitrite or elevated nitrate, so appearance is not a substitute for measurements. Test again when fish behaviour changes or after stocking and feeding increase, because both changes place additional demand on the filter.

The weekly routine joins water replacement, waste removal, testing and filter inspection into one decision cycle. Results from one week establish a comparison for the next, making an upward nitrate trend or loss of filter flow easier to recognise before it develops into a larger welfare problem.

Feed one measured meal each day

OATA describes tetras and pencilfish as omnivorous and recommends a good-quality flake or granule as the everyday food. Small live or frozen items such as daphnia, small bloodworm or tubifex can be included for variety. Match the particle size to fish from the selected dispatch grade so they can take the food promptly.

Judge the portion by consumption rather than by a fixed pinch for every aquarium. Add a small amount, watch the group feed and stop adding food once the amount that can be eaten within a few minutes has been reached. The correct portion changes with the number of fish, their dispatch size and the other animals sharing the meal.

Overfeeding creates a water-quality problem as well as wasting food. Uneaten material breaks down and releases toxic waste into the water, increasing the burden on the biological filter. A larger shoal therefore needs a portion adjusted to its numbers, but it still does not need food left on the substrate after the feeding period.

Use feeding as a daily observation point

Watch the whole group during its daily meal. Reduced intake or a loss of interest in food is one of the changes OATA identifies as a possible health warning. Compare behaviour across the group: a single fish repeatedly failing to feed deserves attention even if the rest finish the portion.

Keep variety within the named food types rather than allowing treats to displace the complete staple. Flake or granule supplies the regular meal; the small live or frozen choices add variation. Maintain the once-daily schedule and use weekly water tests to check that feeding and filtration remain in balance.

Introduce the group with a first-month plan

Prepare the aquarium around the complete intended group before any fish are introduced. Confirm that the filter is mature, ammonia and nitrite are zero mg per litre, the measured water falls within the chosen planning ranges and the aquarium can accommodate at least five Cochus Blue Tetras at the 5.4 cm adult planning size.

Increase the aquarium population slowly. Beneficial bacteria need to expand whenever fish numbers and feeding rise, and stocking too quickly can lead to new tank syndrome. If other residents are already present, include them when judging the additional waste load rather than treating the tetra group as the aquarium’s only demand.

Before introduction

• Test ammonia and nitrite and proceed only when both read zero mg per litre.
• Confirm temperature, pH and hardness against the chosen aquarium window.
• Check that filtration is operating without a blockage.
• Count the intended same-species group and assess the aquarium at adult size.
• Review every resident using the compatibility screen before combining them.

During the first week

Use the once-daily feed as a structured observation point. Healthy fish should have clear, bright eyes, intact scales and undamaged fins, with no ulcerations or bumps. Watch for hanging at the surface, sitting on the bottom, erratic swimming, unusual hiding, a marked colour change, altered breathing, white spots, fluffy growths, damaged fins or scales, and reduced interest in food.

Complete at least the normal weekly water test even if behaviour looks typical. If any warning appears sooner, test immediately rather than waiting for the scheduled maintenance day. Compare ammonia and nitrite with the required zero reading and check nitrate against the tap-water baseline.

Through the first month

Repeat the weekly cycle of testing, a 25% partial water change at least once every week, substrate siphoning and filter inspection. Keep feeding to one meal consumed within a few minutes. Delay further livestock additions if ammonia or nitrite rises, filter flow falls or the existing group shows a health change.

If behaviour, breathing, appearance, body condition or feeding changes, test the water first and contact us for health guidance. These signs identify the need to investigate; they are not a diagnosis and should not be matched to a treatment by appearance alone.

Screen every tank mate by adult size and behaviour

Begin with adult size. OATA advises that smaller tetras should not be housed with fish large enough to eat them, so avoid any resident capable of swallowing a Cochus Blue Tetra. Make that judgement using the tetra’s 5.4 cm maximum total length and the prospective companion’s adult size, not the size of either animal on the day it is introduced.

Next compare temperament and water requirements. Tetras and pencilfish mix best with species of similar size and temperament, but that statement is a screening rule rather than a universal list of companions. The candidate must also fit the same temperature, pH and hardness window without either animal being held at an unsuitable edge of its range.

OATA warns that larger or more boisterous tetra species may nip timid or long-finned fish. That warning does not make every tetra a fin-nipper, but it gives a clear observation rule. If chasing, fin damage, increased hiding or a change in aggression appears, reassess the combination and the space rather than relying on the general reputation of the fish involved.

Water overlap must be checked with measured values. For example, calling two residents freshwater tropical fish does not show that their pH and hardness needs overlap. Compare their stated ranges with the aquarium’s actual readings, then confirm that ammonia and nitrite remain zero after stocking.

A species name alone cannot predict every interaction because individual behaviour and aquarium conditions vary. Screen the adult size, temperament, water overlap, social needs and total capacity together, then continue observing after introduction.

Count the whole community before setting the quantity

Apply the social minimum to the Cochus Blue Tetras themselves: keep at least five, with more being better where space and filtration allow. A mixed aquarium containing several unrelated small fish does not change the number of this tetra being planned. Set the purchase quantity deliberately because each quantity supplies one individual animal.

Use simple count checks

Then calculate space from adult size and total population. FishBase records a 5.4 cm maximum, placing this animal just above the 5 cm threshold for which OATA recommends at least an 80-litre aquarium for a small shoal. Treat 80 litres as a starting planning reference, not as permission to add an unlimited number of residents.

Include every fish in the capacity decision. An aquarium with five Cochus Blue Tetras and no other residents places a different demand on filtration from the same aquarium containing an established community. Food entering the tank, waste production, swimming space and shelter all change as animals are added.

Do not use dispatch size to justify temporary crowding. A 2 cm animal still grows towards the same adult planning figure, and a group purchased at a smaller grade still needs its long-term space from the start. Planning once around adult size avoids having to solve a predictable capacity problem later.

For a stocking and compatibility assessment, contact us with the aquarium’s measured volume, temperature, pH, hardness, ammonia, nitrite and nitrate, plus the species and numbers already present. Those details allow the proposed group to be assessed as part of the whole aquarium rather than in isolation.

Answer the key questions before choosing

What is a Cochus Blue Tetra?

Boehlkea fredcochui is a freshwater characin from the Amazon Basin. FishBase places it in Stevardiidae and records a maximum of 5.4 cm total length.

Does one purchase of a Cochus Blue Tetra supply one animal?

Yes. One purchase quantity supplies one animal of the selected option, so set the quantity to at least five when building the social group described in OATA’s tetra guidance.

Which dispatch sizes can I select for Boehlkea fredcochui?

The dispatch size options are 2 cm, 3 cm and >4 cm. These are dispatch grades; plan the aquarium around the recorded 5.4 cm maximum total length.

What aquarium setup does a Cochus Blue Tetra need?

Use a mature filtered aquarium with substrate, shelter and open swimming space. OATA’s tetra group guidance recommends at least 80 litres for a small shoal of larger tetras measuring 5 cm or more.

Should a Cochus Blue Tetra be kept alone?

No. OATA’s tetra group guidance advises keeping tetras in groups of at least five, with more being better where the aquarium’s space, filtration and total stocking allow.

What water range should I use for it?

OATA’s tetra group guidance gives 22–27°C, pH 6.5–8.0 and 4–12°dH for aquarium planning, with ammonia and nitrite at zero mg per litre; FishBase records 22–26°C for the species.

What should this fish eat?

OATA’s tetra guidance says to feed a good-quality flake or granule once daily, with small live or frozen daphnia, bloodworm or tubifex for variety. Give only what the fish consume within a few minutes.

How should I prepare for its introduction?

OATA’s tetra guidance says to prepare a mature filtered aquarium, confirm ammonia and nitrite are zero mg per litre, check the other water values and increase the population slowly so the biological filter can adjust.

Which fish can live with it?

OATA’s tetra guidance says to choose species of similar adult size and temperament whose water needs overlap. Avoid fish large enough to eat it, and use caution around timid or long-finned residents if boisterous behaviour or fin-nipping is seen.

References used for species and husbandry details

• FishBase: taxonomy, family, freshwater environment, distribution, environmental ranges, maximum recorded length and conservation category.
• Wikipedia: concise natural history and Amazon Basin range.
• Ornamental Aquatic Trade Association: tetra husbandry, social numbers, aquarium planning, water values, feeding, maintenance, introduction and compatibility.
• RSPCA: biological filtration and the conversion of ammonia through nitrite to nitrate.
• Tropical Fish Co delivery policy: delivery arrangements and Live Arrival Guarantee terms.