Gälar

Gälar are the Swedish term for gills, the respiratory organs used by many aquatic animals to extract oxygen from water and release carbon dioxide. In Swedish zoological usage, gälar is the plural form of gäl.

Anatomy and structure: In fishes, gills are arranged on gill arches along each side of the pharynx. Each arch bears gill filaments, which in turn carry lamellae—thin, plate-like structures that maximize surface area for gas exchange. Water is typically pumped over the gills by mouth and hyoid muscles or specialized pumps, while blood in the gill capillaries flows in the opposite direction in many species, enabling efficient oxygen uptake through counter-current exchange. In most bony fishes, the gills are protected by a bony flap called the operculum, which helps regulate water flow. In cartilaginous fishes such as sharks, gill slits are exposed and water must flow over each slit.

Variation and development: Gills are supported by a series of gill arches on each side of the pharynx, with gill filaments and lamellae increasing surface area for gas exchange. Some species possess gill rakers, which help prevent food particles from entering the gills. Amphibians show variation as well: many larvae have external gills, while others develop internal gills or lose gill tissue as they mature.

Function and ecology: Gills enable aquatic animals to obtain dissolved oxygen and regulate carbon dioxide and pH balance in their blood. Their efficiency depends on water oxygen content, flow, temperature, and the animal’s metabolic rate. Gills can be affected by pollution, sediment, and low-oxygen conditions, making them important indicators of aquatic health.