A study of larval fishes in the Lower Mississippi River, river miles 505-525, was conducted from April through October 1980. The objectives of this study were to assess the relative importance of dike fields, revetted banks, and other habitats to fish larvae and to characterize the seasonal changes in local distribution of ichthyoplankton within a dike field. With respect to larval fish exology, the results of this study may be representative of the Lower Mississippi River mainstream in general. Shads and herrings were abundant and common in all locations, while other taxa exhibited clear affinities for certain habitats. The Lower Cracraft Dike Field exhibited variability in larval fish diversity and abundance throughout the spawning season. During high to moderate river stage conditions (April through June), larval fish diversity was high and abundance was greater at open water stations than nearshore stations.

Larval fish were collected in the Lower Mississippi River from 8 March to 13 November 1978 to describe variations in diversity and abundance of larval fish among nine types of habitats for the entire spawning season, investigate diel fluctuations in diversity and abundance, and evaluate replicate sampling procedures. The abandoned channel and oxbow lake habitats had similar larval populations; these habitats showed relatively low diversity and high densities of clupeids and centrarchids. Natural banks and revetted banks had high and similar diversities and abundance of larval fish. There were considerable variations in density and diversity among the four revetted bank stations sampled. The dike field habitat was characterized by a high diversity and moderate density of larval fish. All families of larval fish collected during the entire study were represented in the dike field habitat. The diversity and density of larval fish differed greatly among the six dike field stations sampled. Three of the four main channel stations sampled showed low diversity and density of larval fish. The fourth main channel station had high diversity of larval fish and high densities were observed on two sampling dated. Density of larval fish was low but diversity of larval fish was relatively high in the temporary secondary channel habitat. Density and diversity of larval fish were low in the permanent secondary channel and the sandbar habitats. A variance component analysis demonstrated that samples taken within a 1- to 2-hr time period of a diel cycle did not constitute significant (probability