To survive, grow and reproduce, fish, like all heterotrophic animals, need food and oxygen. However, while a huge literature exists on the food and feeding habits of fishes (accommodated within FishBase through several tables and graphs), much less exists in the literature on the organs and processes which allow energy to be extracted from this food.

The essential process is respiration, and it is accommodated, in part, in the OXYGEN table. The important organs¾ the gills¾ are dealt with in the present table.

This table presents the overwhelming majority of measurements of the gill area in fishes so far published, i.e., of the surface area that limits their oxygen intake and hence their metabolic and growth rates (Pauly 1979, 1981, 1994). Most of the measurements stem from the compilations of Hughes and Morgan (1973), De Jager and Dekkers (1975), and Palzenberger and Pohla (1992).

Hughes (1984) discusses some of the problems related to gill area measurements, and their interpretation, and this work should be consulted before analyzing the information in this table. Pauly (1979, 1981, 1994) and Longhurst and Pauly (1987) present the elements of a theory of fish growth from which hypotheses can be derived that can be tested using gill area measurements; practical uses of such measurements include pollution and ecotoxicological studies.

Fig. 54 shows that gill area in fishes increases with body weight, though the slope of the log-log plot of less than 1 implies that relative gill area must decrease with body size.

Fig. 55 shows relative gill area, plotted against body weight. As expected, this log-log plot shows that relative gill area declines with body weight, with a slope of about -0.2. However, this plot masks species-specific differences, which are important when the relationship between gill area and growth is studied (Pauly 1981).

Accounting for these differences requires consideration of swimming modes and/or caudal fin aspect ratios. We expect to have, in FishBase, a graph directly linking growth performance and gill area, and taking these extraneous factors into account.

Also, the contents of this table will be updated, using appropriate references, and your suggestions concerning this are welcome.

The key field of this table is the Gill area (in cm²), which must always be related to Body weight (in g).

A field for a derived variable, Gill area/body weight (cm²/g) is also available, as well as for the blood/water distance, i.e., for the thickness of the gill epithelium (in nm).

A Remarks field allows for methodological or other comments.

You get to the GILL AREA table by clicking on the Biology button in the SPECIES window, the Morphology and physiology button in the BIOLOGY window, and the Gill area button in the next window.

On the Internet, you get to the GILL AREA table by clicking on the Gill area link in the ‘More information’ section of the ‘Species Summary’ page. You can create a list of all species with available data by selecting the Gill area radio button in the ‘Information by Topic’ section of the ‘Search FishBase’ page. If you select a family and the Graph radio button in the ‘Information by Family’ section of this page, you can create Gill area graphs for various families.

I thank Professor G.M. Hughes for his willingness to answer, over the years, my various queries about fish gills.