The sturddlefish is a

hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...

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 only living species of paddlefish (Polyodontidae). This family is most closely r ...

(''Polyodon spathula'') and the

Russian sturgeon The Russian sturgeon (''Acipenser gueldenstaedtii''), also known as the diamond sturgeon or Danube sturgeon, is a species of fish in the family Acipenseridae. It is found in Azerbaijan, Bulgaria, Georgia, Iran, Kazakhstan, Romania, Russia, Turkey ...

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

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

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 Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the egg. Th ...

, a type of

parthenogenic Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...

reproduction where a sperm cell must be present to trigger

embryogenesis An embryo is an initial stage of development of 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 sperm ...

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. Currently, all living hybrid fish are living in captivity at the research lab in Hungary. There are no further 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 and 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

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-J ...

, 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 likely extinction of the Chinese paddlefish in 2019. Sturgeons are considered by

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

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 Sterile or sterility may refer to: *Asepsis, a state of being free from biological contaminants * Sterile (archaeology), a sediment deposit which contains no evidence of human activity *Sterilization (microbiology), any process that eliminates or ...

, as is the most frequent outcome for hybrids with distantly related parents.

Potential

The hybrid fish may have potential uses to reduce the

carbon footprint A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbo ...

and cost of feeding farm fish cultivated for

caviar Caviar (also known as caviare; from fa, خاویار, khâvyâr, egg-bearing) is a food consisting of salt-cured roe of the family Acipenseridae. Caviar is considered a delicacy and is eaten as a garnish or a spread. Traditionally, the ter ...

production among other things. However, due to likely being sterile as hybrids, this is most likely not an option. As a result 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