FUNCTIONAL-MORPHOLOGY OF GILLS AND RESPIRATORY AREA OF 2 ACTIVE RHEOPHILIC FISH SPECIES, PLAGIOSCION-SQUAMOSISSIMUS AND PROCHILODUS-SCROFA

Measurements of gill dimensions were carried out on two ecologically d istinct active rheophilic teleost species, the curvina Plagioscion squ amosissimus and the curimbata Prochilodus scrofa, and were analysed in relation to body mass according to the equation Y=aW(b). The gill res piratory areas of P. squamosissimus and P. scrofa were large as expect ed for active fish and increased with increasing body mass (b=0.70 and 0.72, respectively) showing no significant difference between them. H owever, the large respiratory area of both species was realized in a d ifferent way revealing an adaptation to the plasticity of head compone nts related to feeding habits. Consequently, significant differences w ere found between the number and average length of gill filaments and the bilateral area of secondary lamellae. The respiratory area of P. s crofa was due mainly to larger bilateral surface area of the secondary lamellae and its growth coefficient (b=0.51) that was significantly h igher (P<0.05) than that found for P. squamosissimus (b=0.36). The fre quency of secondary lamellae mm(-1) of filament was similar in both sp ecies (22+/-2 on one side of gill filament). The dimensions of gill co mponents and the respiratory area of these species suggest a complex i nteraction between head form, and feeding habits related to the functi onal morphology of the gills to meet the oxygen requirements of each s pecies. (C) The Fisheries Society of the British Isles.