Love was in the air during Valentine’s Day this past Friday, which makes this a great week to talk about fish ‘love’. It may be surprising to learn that all fish do not follow one type of reproductive scheme. Many species are broadcast spawners, but this week we highlight some of the more unique fish reproductive strategies with the help of our #SundayFishSketch artists. Keep reading for a look at some evolutionary fish reproductive adaptations!
Spawn and Die
Some salmon, smelt, and capelin among few other vertebrates perform a reproductive strategy called semelparity.
Both males and females of these fishes die almost immediately after spawning. This reproductive strategy uses all these individuals available resources in one large reproductive event. It is hypothesized that the long migrations, changes in elevation and temperature, and transition from saltwater to freshwater are extremely physiologically taxing. The evolution of a semelparous reproduction may have occurred to to the extremely difficulty in returning to the ocean after spawning.
The Asian sheepshead wrasse is just one of many hermaphroditic fish species.
Hermaphrodite (organisms that at one point of another have complete or partial reproductive organs and/or produces gametes of both sexes) fishes come in different varieties. Sequential hermaphrodites are born as one sex but can switch to the other later in life. Generally these can either be protandrous (male to female) or protogynous (female to male). Simultaneous hermaphrodites possess both male and female reproductive organs/gametes at the same time and can often self fertilize.
The Asian sheepshead wrasse is a sequential hermaphrodite. If a school of females has no dominant male, the largest female will change sex to a male (protandry). This is the opposite of clownfishes (see our previous fisheries blog post about Finding Nemo) where if there is no large female, the next largest male will turn into a female.
Beach Spawning by Moonlight
Leuresthes sardinas, affectionately called the Grunion, are a species of New World silverside in the family Atherinopsidae.
These little fish live off the eastern coast of North and Central America and perform a unique mating act. Approximately two to six nights after the full and new moon, female grunion will make their way onto sandy beaches along the California coast and bury their tails in the sand to lay their eggs. Males make their way onto the beach and wrap themselves around females and deposit their sperm.
Locals in the area usually broadcast the approximate timing and location that grunion are expected to spawn and many people will visit these beaches to catch them during their ‘Grunion Run.’
Fishes have evolved multiple types of parental care, many of which involve care of offspring by the father (paternal) and not the mother (maternal). This can come in many forms including nest guarding, but today we focus on male fish brood pouches.
Many male seahorses and pipefish of the order Syngnathiformes have evolved brooding pouches. Females deposit eggs into the opening in the male’s brooding pouch after which he closes up the pouch seam and then releases his sperm directly onto them. Males supply the embryos with nutrients as they develop in the pouch over multiple weeks. When ready, the male opens up the pouch and forces the young out.
A Mouth Full of Love
Opistognathus aurifrons, or the yellowhead JAWfish, gives us another example of unique fish reproductive strategies.
These small coral reef fishes are known as mouth brooders, a reproductive strategy that has evolved multiple times in fishes. These fish brood their offspring by holding them in their mouths. This behavior isn’t restricted to only males or females, as depending on the species either sex has been witnessed performing this behavior.
In the yellowhead jawfish, the male carries the eggs in his mouth until they hatch. Although fish with this behavior usually produce smaller clutch sizes, this is offset by the higher chance of survival of each individual offspring due to the protection given by the parent.