Fertilization: The Ultimate Race
Maria Goller, Amanda Cox, Phil Visser, Ty Bailey
Utah State University
Introduction
Fish use a variety of different methods of fertilization including internal and external fertilization, as well as some extreme
forms such as buccal (mouth) fertilization. The majority of fishes engage in external fertilization, which can occur
simultaneously, with both male and female releasing gametes at the same time, or asynchronously, with one of the sexes
releasing gametes first (Balon 1981). External fertilization is often broadcast fertilization, found in 75% of marine teleosts,
when many individuals of both sexes come together and release their gametes (Anonymous). Internal fertilization is common
in Chondrichthyes, and is also found in coelacanths, surfperches, and scorpion fishes (Budy 2012).
Figure 1. Mandarin fish
(Synchiropus splendidus)
are a species that mates
internally.
Buccal fertilization
In the catfish genus Corydoras, the
female will “drink” the male’s sperm,
which then passes through her digestive
system and fertilizes her eggs (Budy
2012). These species are able to gulp air,
which is transferred through the
digestive system into the intestine.
Sperm pass quickly through the intestine
using the same method (Kohda et al.
1995).
Delayed fertilization
Figure 2. Example of a Corydoras catfish, the Leopard Cory, Corydoras trilineatus.
Internal fertilization
Most sharks use internal
fertilization. This requires an
intromittent organ in the males to
allow sperm transfer, such as in the
form of claspers from modified
pelvic fins (Helfman et al. 2009).
Mating is very difficult since
individuals must be swimming
constantly to breathe and the
medium makes contact difficult to
maintain.
Figure 3. Sharks engaged in mating (internal fertilization), which is complicated
underwater.
Images
Figure 1. “Mandarin Fish Mating.” Manta Ray Bay Resort. Accessed 23 Nov. 2012. <http://www.mantaray.com/images/diving/sidebar/mandarine_fish_mating.jpg>
Figure 2. “Leopard Cory (Corydoras trilineatus).” The Planted Tank. Jelsoft Enterprises Ltd. 2012. Accessed 23 Nov. 2012.
<http://www.plantedtank.net/forums/myFish.php?do=view&p=127&n=Leopard_Cory_Corydoras_trilineatus>
Figure 3. “Port Jackson Sharks mating #2.” Australian Museum. Disqus. Accessed 23 Nov. 2012. <http://australianmuseum.net.au/image/Port-Jackson-Sharks-mating-2/>
Figure 4. “Dwarf Surfperch, Micrometrus minimus.” Mexfish.com. 2011. Accessed 23 Nov. 2012. <http://www.mexfish.com/fish/dsperch/dsperch.htm>
Figure 5. "Painted Goby.” Green Packs. 2011. Accessed 23 Nov. 2012. <www.greenpacks.org/2009/04/09/shooting-the-underwater-delights-off-the-british-shores>
References
Anonymous. Chapter 1: Fish Reproduction. University of California Press. 9-37. Accessed 23 Nov. 2012. <www.ucpress.edu/content/chapters/9317.ch01.pdf>
Balon, E.K. 1981. Additions and amendments to the classification of reproductive styles in fishes. Env. Biol. of Fishes 6 (3/4): 377-389.
Budy, P. 2012. Reproduction. October 25, 2012. Fish Diversity WATS 3100.
Helfman, G.S., Collette, B.B., Facey, D.E., and Bowen, B.W. 2009. The Diversity of Fishes: Biology, Evolution, and Ecology. Wiley-Blackwell, New Jersey. 455-476.
Inhering, R. von. 1937. Oviducal fertilization in the South American Catfish, Trachycorystes. Copeia 4 (1937): 201-205.
Kohda, M., Tanimura, M., Kikue-Nakamura, M., and Yamagashi, S. 1995. Sperm drinking by female catfishes: a novel mode of insemination. Env. Biol. of Fishes 42 (1995): 1-6.
Marconato, A., Rasotto, M.B., and Mazzoldi, C. 1996. On the mechanism of sperm release in three gobiid fishes (Family Gobiidae). Env. Biol. of Fishes 46 (1996): 321-327.
Warner, R.R. and Harlan, R.K. 1982. Sperm competition and sperm storage as determinants of sexual dimorphism in the dwarf surfperch, Micrometrus minimus. Evolution 36(1): 44-55.
Summary
In some species, females may store sperm for
up to a year before fertilizing the eggs
(Warner and Harlan 1982, Inhering 1937).
This method of internal fertilization is unique
because fertilization occurs without the
male’s presence. Examples are the dwarf
surfperch and the catfish, Trachycorystes
striatulus. T. striatulus males also use a
gelatinous plug as an attempt at ensuring
paternity (Inhering 1937).
Figure 4. A dwarf surfperch, Micrometrus minimus. Females may display
delayed fertilization.
Asynchronous external fertilization
In three Mediterranean goby species, the males first form
sperm trails (out of a mixture of mucus and sperm) on the
surface of their nests (Marconato et al. 1996). Females
then come and lay eggs one at a time over the trail. This
mechanism may have evolved to allow the male goby to
guard the nest while the female lays.
Figure 5. The Painted Goby (Pomatoschistus pictus). Males of three
goby species create sperm trails for egg-laying.
Fertilization in water is extremely difficult yet fishes have evolved incredible ways of overcoming the barriers to reproduction. Internal
fertilization is strenuous and energetically very costly, yet effective. External fertilization is also successful, perhaps surprisingly, given that
eggs and sperm must meet in a changing environment.