Algae and Fishes: Benefits and Hazards

Abstract

Aquatic animals such as fish and crustaceans provide human beings with high-quality protein diets. Meals of aquatic animals are based partially or even entirely on algae. Marine algae can be grown as maricultures in marine environments in various forms. Also, algae can be used for fish diets in inland aquacultures. Algae can also be grown not only for their nutritional value but also for their pigments that can affect the colour and health of some aquatic animals thereby affecting their quality and marketability. However, algal phytoplanktons are not massive in large areas of major oceans. The reason behind that lies in the deficiency of iron despite the presence of other major nutrients such as phosphorus and nitrogen in high concentrations. Recently this iron limitation in marine environments attracted the attention of scientists. Thirteen iron fertilisation experiments in those oceans were performed to enrich them with iron which in turn would lead to the increase of the phytoplankton and consequently aquatic animals and fishes. Scientists propose that this would cause mitigation of global warming as algae take in carbon dioxide, the main factor responsible for global warming, and release oxygen during photosynthesis. So double benefits are expected in terms of increasing aquatic animals and decreasing global warming. However, the short and long-term overall effects of those experiments are yet to be validated and evaluated. On the other hand, some algae can have a negative impact on fishes. Toxic algae can cause massive fish mortalities. The two main algal groups responsible for toxins production are cyanobacteria and dinoflagellates. They can spread from one water body to another through ballast water or via biofouling aquatic vessels such as ships and boats. This, in turn, would be harmful and even lethal for aquatic animals and would jeopardize food security. Thereby, surveillance of aquatic vessels must be performed.