Showing papers in "Advances in Marine Biology in 1990"

Plankton Production and Year-class Strength in Fish Populations: an Update of the Match/Mismatch Hypothesis

Abstract: Publisher Summary The degree of match and mismatch in the time of larval production and production of their food has been put forward as an explanation of part of the variability in recruitment to a stock of fish. The magnitude of recruitment is not completely determined until the year-class finally joins the adult stock, and the processes involved probably begin early in the life-history of the fish when both their growth and mortality rates are high. The match/mismatch hypothesis is given in this chapter to cover the subsequent development through larval life up to metamorphosis, and possibly just beyond. The match/mismatch hypothesis has now been extended to the upwelling areas and oceanic divergences equatorward of 40° latitude on the basis that fish in these regions release batches of eggs more frequently when they are well fed and, more generally, that pelagic fish may modify their reproductive strategies such that they can feed and spawn at the same time. A delay in predation is of great importance, particularly when production peaks in early development. This model illustrates the difficulties that occur when growth and mortality are allowed to interact. On the other hand, there are three consequences of the match/mismatch hypothesis that are presented in this chapter. However, the limited conclusion drawn in this chapter is that, investigations of fish larvae should continue to be a part of the study of population dynamics of fishes.

Egg Quality in Fishes

Abstract: Publisher Summary Varying egg quality is one of the limiting factors for successful mass production of fish fry. It may also cause some of the variability in recruitment observed in many wild stocks, since poor egg quality may decrease the survival potential of the hatched larvae. In the literature, the term egg quality has been defined and used in various ways by different authors. Due to the limited knowledge in the field, it has been difficult to pinpoint valid quality criteria. The only definition of egg quality that has general validity is probably the egg's potential to produce viable fry. The egg's potential to produce viable fry is determined by several physical, genetic, and chemical parameters, as well as the initial physiological processes occurring in the egg. If one of the essential factors is lacking, or is incomplete, egg development will fail at some stage. Thus, egg quality should be regarded as determined when the egg has left the female fish and the fertilization process is complete. This definition is, however, of very little practical value, since fry viability obviously cannot be determined before the fry is produced. Good practical criteria for the determination of egg quality should be both possible to identify early in development, and be simple to use. The problems of egg quality have received increasing attention, in relation to cultivation as well as to the assessment of reproduction of wild fishes. This chapter discusses the possible criteria for the determination of quality of fish eggs.

Diel vertical migrations of marine fishes: an obligate or facultative process?

Abstract: Publisher Summary Diel vertical migrations are cyclic changes in the position of aquatic organisms in the water column that occur with 24-h periodicity. Such movements occur at various stages of the development of teleosts, although they are often more evident during the first year of life. Despite frequent study, fundamental questions concerning the nature of diel vertical migrations remain. For example, most life-history traits exhibit phenotypic plasticity in response to environmental factors during the development. From the fisheries viewpoint, an understanding of diel vertical migration is critical for surveys of abundance at all life-history stages. Such surveys of exploited populations of adult fish have long been employed during the stock assessment process and are becoming increasingly significant, particularly, in light of the difficulties associated with obtaining reliable commercial fishery statistics. This chapter presents a review of the studies of diel vertical migration of marine fish species. The extent to which fish exhibit plasticity in their patterns of diel migrations is examined, both with respect to varying environmental conditions and ontogeny. Most importantly, the chapter also assesses whether the patterns of diel vertical migration fits the criteria for endogenous circadian rhythms. Finally, it attempts to address whether the observed diel periodicity in depth occupied is a result of the endogenous effects whereby the periodicity is derived from the fishes' biochemistry or biophysics, rather than more direct effects of environmental stimuli, such as changes in light and temperature providing a cue for certain behavior.

Biology of the Atlantic Halibut, Hippoglossus hippoglossus (L., 1758)

Abstract: Publisher Summary The Atlantic and Pacific halibut (Hippoglossus hippoglossus and H. stenolepis, respectively) are two morphologically similar flatfish forms inhabiting the boreal and subarctic waters in their respective oceans. Until recently, there were disagreements as to the taxonomic status of these two forms. More recent studies, however, using genetically determined electrophoretically detectable protein variants to test for genetic differences, have revealed a genetic difference between Atlantic and Pacific halibut of a magnitude that confirms the treatment of the two taxa as separate species. Pleuronectiform flatfishes are thought to have evolved in the Pacific Ocean in the early Tertiary period because of their greater present-day diversity in the Pacific Ocean. This chapter presents an account of the biology, fishery, and potential for aquaculture of the Atlantic species.

The Development and Application of Analytical Methods in Benthic Marine Infaunal Studies

Abstract: Publisher Summary The purpose of this chapter is to examine the development of practical analytical approaches that have traditionally been applied to benthic soft-bottom macrofaunal (particularly marine) studies. Some commonly applied methods and topics are covered in more detail than others, especially if they are considered to be pivotal in the development of benthic analytical studies. Mensurative studies involve random sampling of the organisms (and related factors) from different stations, selected according to some reasonable survey pattern based on the objectives of the study. The primary aim of all methods discussed here continues to be the simplification of complex patterns occurring in benthic faunal assemblages, such that interpretation and comparison is possible. The key to further progress in this field is to develop sampling and analytical techniques in concert. This presupposes that research aims and study hypotheses can be more clearly stated in benthic studies than has often been the case in the past.