A comparative study of pelagic and demersal eggs from common marine fishes in Northern Norway

Morphology and structure, as well as physiology and composition of marine teleost eggs have been studied. Spawning season and developmental rates of the eggs have also been included. Eggs from cod (Gadus morhua), haddock (Melanogrammus aeglefinus), halibut (Hippoglossus hippoglossus), long rough dab (Hippoglossoides platessoides), plaice (Pleuronectes platessa), flounder (Platichthys flesus), capelin (Mallotus villosus), herring (Clupea harengus), lumpsucker (Cyclopterus lumpus), father lasher (Myoxocephalus scorpius), and catfish (Anarhichas lupus) were compared. This paper presents new results and a review of the authors' earlier work. Although differences were observed between closely related species, the largest differences were found between pelagic and demersal eggs. Pelagic eggs generally have a thin, homogeneous, lamellated chorion; their yolk is homogeneous, they cleave relatively fast and hatch within 14–26 days (at 50° C). Demersal eggs usually have a thick, more complex chorion which is more resistant to mechanical damage. The yolk contains many oil droplets, these eggs are generally characterized by a relatively high lipid content. Some demersal eggs develop relatively slowly, taking more than one month to hatch, but do so at a more advanced stage than pelagic eggs. Others, e.g. halibut eggs, hatch at a very premature stage. Osmotic measurements showed that there is no clear difference in osmotic properties between pelagic and demersal eggs.