Early morphological development of gills in smallmouth bass (Micropterus dolomieui)

Abstract

The morphological development of the gill apparatus in 11- to 180-day old smallmouth bass (Micropterus dolomieui) is described as seen by scanning electron microscopy. Filament protrusions without lamellae developed on the midregion of the gill arches in yolk-sac fry. Filament development progressed from the midregion of the gill arch toward the insertions. Secondary lamellae were first observed 15 days after egg fertilization when the fry became free swimming. Lamellae first appeared on filaments proximal to the gill arch and advanced distally. Proliferation of filaments and lamellae continued through at least the first 90 days of life. Filaments on the medial hemibranch of a holobranch were longer than those on the lateral hemibranch for at least the first 90 days. Filaments were alternately arranged between two hemibranchs of a holobranch. Substantial differences existed between gill developmental stage at hatching in smallmouth bass and that previously reported for salmonids. The dynamic nature of the developing gill indicated that quantitative descriptions of filament length, lamellar number and area, and total gill surface area requires examination of specimens at numerous different ages. This is the first morphological description of developing gills in a teleost fish based on observations by scanning electron microscopy.