Sometimes strange holes are discovered in aquatic plants, or whole shoots are suddenly 'defoliated' so that only bare stems remain – a phenomenon that occurs above all with mosses, ground cover plants or fine-leaved aquarium plants. The first assumption is then usually that the plant is suffering from a deficiency symptom. This is not always the case, though. Plant-eating animals can also have caused the damage.

Feeding damage on large-leaved aquatic plants

A typical example is when plecos such as the blue bristlenose pleco are kept together with large-leaved aquatic plants of the Echinodorus type in a community or South America aquarium. If the catfish lack plant-based food, it is quite possible that they will then start eating the leaves of the Echinodorus plants. This often shows up as perforated leaves whose surface looks roughened and frayed. The holes are not clearly delimited and perfectly round, however, but have rather ragged edges. These damages are often mistaken for a deficiency symptom, and the cause is then sought in inadequate plant nutrition. Holes caused by nutrient deficiency, however, usually have a clear structure and are less frayed. The boundary between hole and leaf is much clearer than with feeding damage. In some cases there is a ring-shaped lighter discoloration around the hole (see photo below); this is then a nutrient deficiency.

Holes in the leaves, here not feeding damage but a deficiency symptom.

Algae infestation and feeding damage

A typical example of the combination of feeding damage and algae infestation is the appearance of fur algae or fuzz algae that settle on the leaves of aquatic plants. A similar effect can also occur with green spot algae or general algae coatings. Algae eaters in the aquarium, especially Amano shrimp, begin grazing the algae off the leaves. If the plants have soft leaves, they are affected by the shrimp's claws, so that the leaves are perforated or even partly eaten along with the algae.

Species such as Hydrocotyle tripartita or red-leaved stem plants such as Alternanthera reineckii 'Mini' are frequently affected. This feeding damage was not caused by the algae eaters out of malice at all, since the animals are after the algae on the leaves. The perforated plants are then rather collateral damage. Hard-leaved species such as Anubias are almost never affected, since they can withstand being grazed on by the shrimp.

The interplay of deficiency symptoms and feeding damage

It is not that rare for the phenomenon to occur in the aquarium that an aquatic plant suffers from certain deficiency symptoms. These often show up as small holes or other kinds of necrosis in the leaves, caused by a lack of carbon or macronutrients. You may not notice the small damage that already exists at first, but plant-eating animals do notice it. They now start at the holes in the leaves and eat the leaves from there. This creates even larger holes and damage, which now look considerably more frayed. In some cases only the skeleton of the leaves is left. At the latest now the damage becomes clearly visible, but cannot be attributed unambiguously.

Fish

Source and copyright: Dances - Own work via Wiki Commons, License: CC BY-SA 3.0.

If fine ground cover plants (such as Hemianthus species) or fine-leaved mosses are present in an aquarium, you sometimes wonder about their poor growth. The plants look stunted, and in some cases only small bare stems without foliage can be seen. This is then mistaken for a deficiency symptom. If certain ornamental fish or an overpopulation of shrimp are present, however, they may have damaged the plants. This includes above all algae-eating animals such as Siamese algae eaters, reticulated Siamese algae eaters, or garra species (e.g. Garra rufa). These fish are often acquired as useful animals to eat black beard algae or thread algae. Usually you do not suspect these aquarium inhabitants of also eating plants, since you almost never catch them in the act. Field reports do confirm the incidents, however, as do A/B comparisons when you then keep such planted aquariums under the same conditions without these animals. The fine-leaved plants recover again without this animal stock.

Snails on java fern tips

Copyright by Roland Emmenlauer

The shoot tips of java ferns stand out because they visually have a different shade of green than the rest of the fern's leaf. At the front tip the green is darker and more transparent. The tissue in this growth zone is probably also somewhat softer than in the rest of the leaf. Some snail species such as ramshorn snails can go after these shoot tips and nibble on them when there is a corresponding lack of food. The rest of the leaf tissue is usually too hard and is left alone. A remedy here is targeted supplementary feeding of the animals with greens or a reduction of the snail population.

Preventing feeding damage on aquatic plants

When aquarium animals go after aquatic plants, they obviously have a need for plant-based food. Plant-eating animals are often kept in the aquarium as useful animals to curb algae growth. Beyond that, though, such creatures also need other plant food, and if it is not available, they will take it elsewhere. Targeted supplementary feeding with suitable greens therefore helps. It is a common remedy in the aquarium hobby to give appropriately prepared vegetables. For example, blanched spinach, cucumber or zucchini in organic quality can be fed. The vegetables should be untreated and free of pesticides. Leftover food should be removed after a few hours so that it does not pollute the water. Do you want to learn more about the topic? Then take a look here.

It should also be mentioned, however, that some predominantly plant-eating animals also need animal protein now and then. These include, among others, Amano shrimp or certain catfish species. Frozen and live food can be used well here, but should be fed sparingly.