EL CENTRO – It’s mating season at the Biological Control Unit of the Imperial Irrigation District.

Located in an industrial area behind the steam plant at the corner of Dogwood and Villa roads, BCU is one of IID’s lesser-known companies. It’s actually a fish farm, and on this farm a small group of workers are raising a species of Asian carp known as grass carp.

A grass carp essentially does what its name suggests: it eats vegetation – in this case, vegetation that could potentially obstruct the IID’s extensive channel system.

In 1981, IID began a three-year study of the mechanical, chemical and biological methods of controlling hydrilla, a fast-spreading aquatic plant that has become a serious local problem for canals and supply systems. in water in the late 1970s.

The results concluded that mechanical methods were temporary and expensive, and chemical methods were incompatible with agricultural and fishery use. Biological research conducted in cooperation with Coachella Valley Water District has shown that the most economical and efficient way to solve the problem is to introduce the sterile grass carp to eat.

The IID hatchery was completed in May 1988. In June 1989, the United States Department of Agriculture awarded the district a Distinguished Service Award for outstanding achievement in pioneering biological hydrilla control. In addition to hydrilla, grass carp also feed on aquatic grasses such as pondweed sago and Eurasian water milfoil.

The two important caveats to using these carp as weed eaters are to make sure they are sterile and to make sure they are not dropped just anywhere. Grass carp are very good at what they do. They can consume many times their own weight of vegetation each day and, if left unchecked, can crowd out other species and upset the ecological balance of aquatic habitats. This is why state law prohibits the use of non-sterile grass carp, but allows certain strict and limited uses of sterile grass carp with the proper permission of the California Department of Fish and Game.

The IID’s BCU is the only licensed sterile herbivorous carp hatchery in the state, and the actual hatch occurs within the few weeks of spring that constitute the carp spawning season. In the wild, carps do what they will, but at BCU their breeding is very controlled.

Hatchery operations coordinator Pablo Cortez and his team on Friday collected eggs and sperm from two females and four males of grass carp. Each female was paired with two males in the breeding process. During this process, they are kept in small tanks inside the hatchery. Brooded females each receive a series of three hormone injections to prepare them to release their eggs, while males each receive a single hormone injection. The last injection for females is given approximately 12 hours before their eggs are collected.

Cortez carefully monitors the females to try to determine if they are ready to release their eggs. This part of the job is more of an art than a science because fish don’t always follow the clock. Females also weigh up to 40 pounds and are not sedated, so they fight.

Friday’s first hen was no exception. After being pulled from her tank with a net, she was wrapped in towels to help her secure and placed to the side and held comfortably. She was then stimulated to release her eggs into a large glass beaker.

According to Cortez, Friday’s first patient was a bit stingy, releasing perhaps half as many eggs than he normally expected. However, there is no second chance. “You get what you get,” he said.

The same goes for males, although in their case the collection process is a little less painful as they are sedated and the volume released is much smaller.

Once the harvest of a trio of fish is complete, a quantity of eggs is poured into a cake pan where it is gently mixed with the sperm of the two males. Timing is of the essence at this point, as this is the part of the process when BCU staff attempt to ensure that newborns from this union will not be able to reproduce.

The fertilized eggs are poured into a hollow steel cylinder buffered at the bottom with water. More water is added to complete the cylinder, then it is slipped through a hydraulic press. Starting four minutes after the carp eggs are fertilized, 8,000 pounds of pressure is applied to the contents of the cylinder for exactly 90 seconds.

The reason for this, Cortez explained, is to mutate the fertilized eggs and add a third set of chromosomes. The presence of this “triploid” chromosomal structure makes the fish sterile.

After the pressurization process is complete, the eggs are transferred to one of the sets of hatching stations. If all goes well, hundreds of small fry will be born in about 30 hours. If that doesn’t work, the process may not work.

The minimum goal each year is to spawn 12,000 to 15,000 triploid carp for release into the IID channel system. Of course, Cortez and his team can’t believe the carp they’ve bred are triploid. They test the blood of each fish before it is released.

IID also sells carp for vegetation control purposes in other areas, such as Yuma. Grass carp that are sold are equipped with a tracking chip to make sure they don’t end up in a place they don’t belong.

One place where grass carp is prohibited is in a fisherman’s bucket. State law prohibits athletes from taking or possessing grass carp at any time. Any grass carp caught by accident must be immediately returned to the water safe and sound. The penalties are severe and can include both prison terms and fines.

Arturo Guzman has worked at BCU for 19 years. He applied for the job after previously working for the Imperial Catfish Farm, so he worked around fish most of his adult life.

“I always find it interesting,” he said.