The sturddlefish is a hybrid of the

American paddlefish The American paddlefish (''Polyodon spathula''), also known as a Mississippi paddlefish, spoon-billed cat, or spoonbill, is a species of ray-finned fish. It is the last extant taxon, living species of paddlefish (Polyodontidae). This family is ...

(''Polyodon spathula'') and the Russian sturgeon (''Acipenser gueldenstaedtii''), accidentally created by researchers in 2019 and announced in 2020. Obtaining living hybrids through breeding individuals from different

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

is unusual, especially given that the two species' last common ancestor lived 184 million years ago. The hybrids were created accidentally during attempts to induce gynogenesis, a type of parthenogenic reproduction where a sperm cell must be present to trigger

embryogenesis An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male ...

but does not genetically contribute to the offspring. Hundreds of hybrid fish were created, of which about two-thirds survived over one month, and about 100 survived for one year. As of July 2020, all living hybrid fish are living in captivity at the research lab in Hungary. There are no current plans to create new sturddlefish.

Background

Both the American paddlefish and the Russian sturgeon are

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

. Researchers in Hungary conducted experiments designed to test if either species could be bred in captivity. As part of these experiments, an attempt was made to induce gynogenesis with each species. During the course of the experiments, the researchers used sperm from paddlefish fathers instead of sperm from sturgeons to act as a control in the fertilizing of female sturgeons. The researchers were surprised when viable offspring resulted. The two species share a most recent common ancestor which lived in the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

, approximately 184 mya. For this reason, the potential for a hybrid between these two species was not initially considered by the researchers, who later speculated that in spite of the long time span that there were relatively few genetic changes between the species. Both fish have been called "living fossils" due to their slow evolution over time. The American paddlefish is the only species of paddlefish living after the extinction of the Chinese paddlefish, which was estimated to be extinct by 2005, and no later than by 2010. Sturgeons are considered by

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

to be the most critically endangered group of species in the world based on over 85% of sturgeon species being at risk of extinction.

Description

Two distinct groups of hybrids were formed. Individuals in the first group have approximately equal amounts of DNA from each species, and display approximately equal amounts of physical characteristics from each parent. Members of the other group contained approximately twice as much sturgeon DNA due to chromosome doubling, and for this reason have physical appearances more similar to sturgeons. It is expected that the sturddlefish hybrids will be sterile, as is the most frequent outcome for hybrids with distantly related parents.

Potential

The Sturddlefish may have the potential to reduce the

carbon footprint A carbon footprint (or greenhouse gas footprint) is a calculated value or index that makes it possible to compare the total amount of greenhouse gases that an activity, product, company or country Greenhouse gas emissions, adds to the atmospher ...

and cost of feeding farm fish cultivated for

caviar Caviar or caviare is a food consisting of salt-cured roe of the family Acipenseridae. Caviar is considered a delicacy and is eaten as a garnish or spread. Traditionally, the term caviar refers only to roe from wild sturgeon in the Caspi ...

production, among other aims. However, due to the hybrids' likely sterilization, that is probably not an option. Because of this, along with the unknown effects that the sturddlefish could have on ecosystems, the researchers who created the sturddlefish have decided not to create more.

References

{{reflist Fish hybrids Sturgeons Fish described in 2020