Below the surface

Forever blowing bubbles

THE sight of a patch of bubbles erupting next to your float is enough to get any anglers heart racing. Knowing a fish is grubbing around down below so close to your hookbait is a magical feeling. But exactly how are gas bubbles made, and what can they tell us?

There are many gasses that dissolve in water. Most will be in a similar concentration to the air above, but this balance can change rapidly thanks to the action of different processes. If gas forms faster than it can be absorbed by the water then a bubble will form.

Sources of bubbles

You will often find aquatic plants covered in gas bubbles after a sunny day. This is the result of photosynthesis, the process by which plants gather the sun’s energy and use it for growth. The gas produced as a by- product of this process is oxygen. Even though oxygen dissolves readily in water, the plants produce so much of it that bubbles form. These can join together until they trickle upwards to the surface and are released. If you see a strand of bubbles rising to the surface over weed then it is likely this is what is happening.

The lakebed is another source of bubbles. As organic matter, such as leaves, break down they release methane gas, which is normally absorbed by the water. If the methane is trapped below the surface of the bottom it will start to build up and can eventually break loose forming bubbles. These bubbles are normally quite large and, if you watch carefully, they will continue to come up in the same spot for quite some time. Often methane bubbles are most prevalent in the summer when the warmer temperatures increase the activity of bacteria in the silt that break down organic matter and release gas.

Normally, methane gas bubbles formed in the silt are released naturally, but fish grubbing around on the bottom can also disturb them and lead to big patches of bubbles hitting the surface in one go, often accompanied by a slick of murky water. These big patches of bubbles are most common in the sheltered corners of lakes where leaves can collect and break down slowly, forming thick organic silt.

These areas can contain high densities of bloodworm and so it is likely that it is these that the fish are feeding on. Because the fish are feeding in the silt they can be quite difficult to catch, as their heads will be buried as they feed on the tiny bloodworm.

Any hookbait on the surface of the silt is likely to be pushed out of the way as the fish feed below.

Bubbles and fish behaviour

Of most interest to anglers are the bubbles produced by fish. These come in two forms and can tell us something about how the fish are behaving. Often fish will release a stream of bubbles after rolling on the surface. All species of fish do this and it is not known whether this is gas accidentally trapped in the mouth and gills after breaking the surface, or whether it is expelled from the swim bladder via a narrow connection at the back of the throat.

The fact that this behaviour is most prevalent when the air pressure is very high may indicate that it is linked to adjusting the gas in the swim bladder. Even species such as pike adopt this behaviour as they top the surface then swim straight back down again.

The more common type of bubbling comes from fish feeding on the bottom and disturbing naturally occurring gas. Some of this gas will be released and will hit the surface in patches of large bubbles, but some will form much smaller frothy bubbles that can tell us more about what is going on below, and which species are responsible.

These smaller bubbles are formed by the gas passing through the gill rakers of fish. The closer packed the gill rakers the more the bubbles will be broken up and the smaller they will be. As a general rule, tiny frothy bubbles will be produced by smaller fish, such as crucian carp. Slightly larger pinhead- sized bubbles by tench and larger bubbles by carp. This can tell us that the fish are feeding in the silt and not necessarily on top it; something to keep in mind when planning your tactics.

Another species that is often responsible for releasing gas are eels. It can be frustrating watching fish producing bubbles over your baited spot thinking that they are carp or tench when, in fact, it’s eels. If you are getting frustrated because fish are bubbling, but you are unable to get a bite, try hooking a worm or maggot hookbait. Very often the culprit will reveal itself as an eel!

Bubbles can tell us a lot about what is going on below the surface, but it is important to not get too hung up on their presence. On harder lakebeds, especially gravel, bubbles may rarely appear, but that doesn’t mean that there aren’t feeding fish to be caught. These very visual signs are just another clue that we can incorporate in our watercraft.