From egg-spitting mothers to “crop circle” nests, here are 10 fish egg facts in time for Easter.

The eggs associated with Easter are usually those of chickens (or made of chocolate!). But this is a time to celebrate new life and the coming of spring; for ABPmer, that means reflecting on lifecycles in the marine environment.

Here are 10 things you (probably) didn’t know about fish eggs:

1. Mouthbrooding (orally incubating) fish must periodically spit their eggs out and quickly suck them back in. This aerates the eggs, and removes waste and fouled eggs to keep them healthy. 

2. Cuckoo catfish eggs incubate in the mouths of other species. The catfish lay eggs in the mouths of female cichlids, which the male cichlid fertilises, thinking they are female cichlid eggs. 

3. Stickleback eggs are fertilised in a nest of plant materials glued together by mucous secretions from the male’s kidneys. 

4. Even within species, salmon eggs range in colour, from pale yellow to dark red, depending on several factors, including water temperature, sediment composition and age. 

5. Killifish eggs can be fertilised and laid by the same parent; the mangrove killifish is a hermaphrodite that is able to fertilise itself. 

6. Large female cod can lay 10 million eggs in a year (although most of these end up eaten, including by cod). 

7. Striped bass eggs require the dissolved oxygen in flowing water to develop into fry. Because of this, mature striped bass migrate from the ocean to tidal freshwater to spawn, so that fertilised eggs can be carried by river currents until they hatch. 

8. One of the few oviparous (egg-laying) shark species, bullhead sharks produce spiral-shaped eggs. This is so the mother can wedge them between rocks or crevices to keep them safe during embryonic development. 

9. Yellow perch lay their eggs in large gelatinous strands, which are then fertilised by multiple males. 

10. Pufferfish eggs are laid in “underwater crop circles”, nests formed by males flapping their fins along the sea floor collect sediment. Made up of a series of peaks and valleys, these formations slow water flow by nearly 25% in the centre where the eggs are kept. 

_{Sources:
(1) Scientific American
(2) Business Insider
(3) Britannica
(4) USGS
(5) BBC [archived]
(6) The Fish Society
(7) USA Today EU; Oklahoma Department of Wildlife Conservation
(8) Natural History Museum
(9) Maryland Department of Natural Resources
(10) Live Science
Image: Silke Baron [CC BY 2.0]}

^{This article was originally published on 06/04/2020, and has since been updated.}

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