Is The Water In Your Aquarium Right For Your Fish?

Fish behavior is obviously influenced by internal motivational factors like hunger and fear, but the components of the aquatic environment fish live in also affect them.

Unlike bodies of water like oceans or rivers, an aquarium is a closed system. In such an environment, components like temperature, metals, and organic substances are not diluted by a constant flow of water but contained, and thus have an even greater impact of fish.

The Temperature In Your Aquarium

Fish are ectotherms. This means that the temperature of their bodies is largely determined by the temperature of their environment.

Temperature changes have a bearing on fishes’ metabolism. Their bodily processes become more sluggish at lower temperatures. Conversely, their metabolism accelerates with a rise in temperature—they will tend to be more active, eat more, and spend more time foraging for food. They may also be more aggressive.

Warmer water has less dissolved oxygen. The loss of dissolved oxygen can suffocate and kill the occupants in your aquarium much faster than higher temperatures will.

Temperature also has a bearing on fish eggs. In the Nile tilapia, it has been observed that the proportion of males in the broods more than doubles when the eggs develop at temperature in excess of 30 deg C.

The Oxygen In Your Aquarium

Fish absorb the oxygen they need for respiration through their gills. When an aquarium is highly stocked or gets choked with overgrowth of plant-life or decaying matter, oxygen levels in the water drop. The situation worsens at night, as photosynthesis ceases and plants start taking up oxygen as well.

Oxygen levels are highest at the water surface where gaseous exchange takes place. Thus, when fish start congregating, and breathing vigorously at the water surface, this is a sign that the oxygen level in the aquarium is inadequate for their needs.

The Chemicals In Your Aquarium

Think of aquarium water as a soup that’s filled with an assortment of chemicals, such as salt and ammonia. Water molecules move from weak solutions to more concentrated solutions through the process of osmosis.

Freshwater fish are essentially parcels of concentrated salt and ion solutions. The molecules in the water, which is a weaker solution, are thus continuously moving into the fishes’ bodies. At the same time, salt continuously diffuses out through the fishes’ gills. To maintain a healthy balance, fish have to keep shedding excess water by producing urine and absorbing salt from the water around them through specialized cells in their gills.

Saltwater fish face the opposite problem. The salt solutions of their bodies are less concentrated than that of their environment. Thus, they are constantly losing water to prevent dehydration.

Any drastic changes in the water chemistry upset this delicate balancing act and throw the fishes’ osmo-regulatory system into chaos, affecting their health and behavior.

Ammonia levels in the water can also influence fishes’ behavior. Experiments using cichlids showed that a slight increase in ammonia led to an increase in their aggressiveness. One possible reason could be that fish interpret the increase in ammonia as an increase in the number of rivals. They therefore respond by becoming more aggressive, preparing to fight off the competitors.

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