上海海洋大学水产与生命学院 The type of eggs 答辩人：魏帅帅

Overview of eggs from various animals Class Types of eggs Development Jawless fish Mesolecithal eggs, especially large in hagfish Larval stage in lampreys, direct development in hagfish Cartilaginous fish Macrolecithal eggs with egg capsule Direct development, viviparity in some species Bony fish Macrolecithal eggs, small to medium size, large eggs in the coelacanth Larval stage, ovovivipary in some species Amphibians Medium-sized mesolecithal eggs in all species Tadpole stage, direct development in some species Reptiles Large macrolecithal eggs, develop independent of water Direct development, some ovoviviparious Birds Large to very large macrolecithal eggs in all species, develop independent of water The young more or less fully developed, no distinct larval stage. Mammals Macrolecithal eggs in monotremes and marsupials, extreme microlecithal eggs in placental mammals Young little developed with indistinct larval stage in monotremes and marsupials, direct development in placentals.

But，today I will introduce the fish eggs！ Think of fish eggs, and you might picture a ritzy dinner party somewhere in Manhattan, where the 1% get together and savor their caviar .Caviar isn’t the final word on fish eggs, though, and there are plenty of options that the rest of us can afford. That’s lucky for us, because the benefits of eating them are amazing. Fish eggs, also known as roe, are an incredible food rich in micronutrients and Omega-3 fatty acids(Omega-3脂肪酸). And unlike fermented cod liver oil (the other fish-derived food so nutritious it counts as a supplement), they’re actually tasty, either plain or as an ingredient in all kinds of recipes.

The basic structure of roe Diagram of a fish egg: A. vitelline membrane B. chorion C. yolk D. oil globule E. perivitelline space F. embryo

The eggs of fish are jellylike Cartilagenous fish (sharks, skates, rays, chimaeras) eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them.

The most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Typically large numbers of eggs are laid at one time and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die.

The type of fish eggs Pelagic eggs 2. Demersal eggs

Pelagic eggs pelagic egg‘s dispersal The upper sun-lit layers of the ocean (epipelagic zone), especially in summer, are literally packed with floating eggs and larvae of many different kinds of fishes and invertebrates. They drift about in the currents, gradually becoming widely dispersed from the spawning grounds.

Pelagic eggs The kinds of fishes that develop floating eggs must be able to produce large numbers of small eggs. A fair-sized hake lays about 1 million eggs; fecundity in cod ranges from 2-9 million eggs; the gadiform genus Molva may produce in excess of 28 million eggs. Mola may produce as max of 300 million eggs

Pelagic eggs The eggs hatch, releasing small, usually colorless larvae that live off the stored reserves in their yolk. When this reserve is used up the larvae begin to feed on tiny phytoplankton and zooplankton. These rich, upper, sun-lit layers are able to support this myriad of developing forms and are appropriately called the nursery grounds of the sea.

Demersal eggs Many eggs are stick to plants, rocks, woody debris, shells, or other hard substrates (e.g., herring, silversides). Some eggs have tendrils or projections that wrap around plants and debris (e.g., flyingfishes). Eggs of the Port Jackson Shark (Heterodontidae) have an augerlike whorl around their exterior. Females lay these eggs in cracks and water motion apparently serves to screw the egg deeper into the substrate. California Grunion (Leuresthes tenuis, Atherinopsidae) spawn on sandy beaches after high tides on dark nights following a full or new moon.

Demersal eggs A few fish species use live invertebrates as a spawning site Marine snailfishes, Careproctusspp (Liparidae), lay their eggs inside the gill chambers of various crabs. Species of bitterling, Rhodeus (Cyprinidae), use freshwater mussels as a spawning site. The male first defends and displays over a particular mussel. The female deposits eggs into the gill chamber of the bivalve using her long ovipositor, after which the male ejaculates over the incurrent siphon of the mussel. Eggs develop inside the mussel and emerge as free-swimming young (Breder & Rosen 1966).

The adaptive values of different fish eggs Pelagic eggs：necessary for successful recruitment because thousands of eggs and larvae are dispersed into areas far beyond the optimal conditions for survival, and thousands die long before hatching or metamorphosis to juvenile stages. As you might expect, these forms are characterized by having wide geographic distributions. Demersal eggs：The purpose of laying eggs in secret places is to protect them from predators

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