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This chapter examines the diversity of eggs and larvae, where it is shown that fish eggs, and in most cases the larvae, are quite different in appearance from the adults, but nevertheless they have distinctive characters that allow for their identification. These egg and larval characters also include systematic information that has been used to imply relationships among fishes, complementing information provided by the adults and from genetic studies. This chapter also discusses the methods and equipment for the morphological identification of fish eggs and larvae and presents examples of the use of larval fish characters in systematics, showing data from selected fish families, viz. the Lightfishes (Gonostomatidae), the Lanternfishes (Myctophidae), the Sculpins (Cottidae), and the Seabasses (Serranidae).

Population dynamics is the study of fluctuations in abundance of populations. It considers how much populations vary, and over what timescales, and seeks to find the causes of these variations. Much of the study of population dynamics in fishes has focused on recruitment, since variations in annual reproductive output of populations seem to drive population abundance in most fishes. Recruitment is the number of juveniles in a population that annually survives the egg and larval stages. This chapter discusses the population dynamics of fishes, focusing on specific topics such as the factors affecting fish egg, larvae, and juvenile survival, causes of fish population fluctuations, and life history of fishes. This chapter also presents the different recruitment studies that have been conducted, discusses the future direction of recruitment studies.

Ecology is the study of the relationships of plants and animals to their environment. This chapter begins by discussing the position of fish eggs and larvae in aquatic ecosystems. It then discusses various topics related to the development of both fish eggs and fish larvae, including the factors affecting their survival and development. The specific topics covered in this chapter include the ecology of fish eggs, the functional morphology of fish eggs and larvae, the importance to fish larvae of spring blooms, the feeding mechanisms of fish larvae and the factors affecting larval feeding, the growth of fish larvae and the measurement of growth, and predation (types and taxa of predators, modes of predation, factors influencing rates of predation, and measuring predation).

This introductory chapter presents a description of the life history stages of fishes, from the egg/embryonic stage to the adult stage, focusing on the early parts of development and growth (early life history) which are the embryonic, larval and juvenile stages. It also presents the types of early life history studies conducted on fishes, including studies done on recruitment fluctuations, population assessment, aquaculture, and conservation studies. This chapter also discusses the integration of basic and applied science, in relation to studies on fish biology and ecology. The concluding discussion of this chapter presents the current literature in the study of early life history of fishes.

This chapter summarizes information on the development of fish eggs and larvae, and introduces juvenile development. The chapter focuses on the changes that occur as the eggs develop, hatch into larvae, and finally transform into juveniles (ontogeny). Most fishes have indirect development; that is, as free-living organisms they go through a number of distinct stages or phases of development (egg, larva, juvenile). This is similar to development in amphibians, but opposed to direct development seen in reptiles, birds, and mammals in which all the free-living forms appear similar and development is largely adding size to the organism. The specific topics covered by this chapter include events that take place immediately after spawning (fertilization and activation), the perivitelline space, rate of development and aging of fish eggs, hatching, notochord and stages of larval development and the transformation stage.