The Biology of Caviar Harvesting

By Dr. I.J. Won, PhD

In nature, the best caviar is produced about a month before spawning. Before that, the eggs are small and immature and, after that, they get soft, mushy, and inedible. The best caviar is defined in shape and has a slight pop in the mouth. Let me explain:

All wild sturgeons are anadromous like salmon: they are born in the river, migrate to the sea to grow up and, years later, return to their natal river for spawning. In the Caspian Sea where Russian sturgeons originate, when the time comes, usually in the spring and fall, the fish start a month-long journey upstream following the Volga River. Through mainly trial and error, fishermen found that the best caviar came from those fish at the journey’s onset, about a month before they reached their natal streams. For this reason, the Russian government allowed their fishermen to catch only those fish that had just started swimming upstream where the Volga meets the Caspian Sea.

That is how Russia produced the best caviar and dominated the world market until the empire collapsed in the 1990s. After that, without the government enforcement, poachers soon flourished, catching any fish anywhere in the water, which eventually led to near extinction of the sturgeon by the early 2000s, when most sturgeon species were declared endangered. This resulted in severe restrictions in legally trading wild caviar.

Necessity is the mother of invention: we soon tried farming sturgeon; a practice called aquaculture. Farmers raise the fish in public waters or private ponds; this is how perhaps 90% of farmed sturgeon are produced. Regulations abound to minimize environmental harm, mainly water pollution via fish poop and uneaten feed resulting from such farms. In response to this problem, we came up with the recirculating aquaculture system (RAS) that keeps the fish in recycled, self-cleaning tanks completely isolated from any surface waters. While it minimizes environmental pollution, the practice requires highly technical and expensive components, comparable to municipal water supply systems that require high capital investment, typically in millions.

Thus ensues an insurmountable problem: we cannot provide the mechanism that anadromous fish need when it’s time to spawn for their own procreation. As they are born and raised in the tanks with nowhere else to go, the old logic that the fish at the onset of their spawning journey has the best caviar is no longer applicable. The fish live in highly protected water at a constant temperature, with abundant food and no competitors or predators, circling around in various tanks for their entire lives.

In this cushy life, the sturgeons lose the sense of time for spawning and, therefore, we have no idea when they may have the best caviar for us. [You may ask why the fish even bother producing eggs under this circumstance, other than the built-in biological instinct.] Again, we resort to gadgets: our main tool for now is the ultrasound machine that doctors use to see progress in pregnancy. We ultrasound every fish, from the age of five or so, at first for their gender; once determined female, they go through periodic checkups for their gonad maturity. That is how we determine when to harvest a fish for caviar.

Most fish start the eggs in a sac made of semipermeable membranes. The eggs are Individually separated in amniotic fluid and when fish ovulate, the entire sac contents spill out into the water where males discharge sperm for spawning. Sturgeons do not have such sacs; instead, the abdominal cavity gets filled with eggs that are individually nourished via blood veins. Imagine a bunch of grapes, each connected via a stem to the main vine; we break the stem to eat each grape. When a sturgeon ovulates, each egg gets separated by breaking its stem and is freely discharged into the water, where it is fertilized by male sperm called milt. When this happens naturally, the eggs are too ripe and mushy to be called caviar, the best-known culinary luxury.

Without breaking the stem, the eggs remain as a connected bunch and, therefore, cannot be massaged or stripped for extraction, the process of producing so-called no-kill caviar. Several biologists came up with a trick: to strip the eggs without killing the fish, one can induce ovulation by injecting hormones to break the stem, much before the fish is ready for natural ovulation. The process is still not commercially widespread because the resulting caviar is soft and mushy. Attempts have been made to firm up the eggs using astringent-type chemicals like borax or similar acids, which are not allowed in the US as food additives. Not having achieved desirable caviar qualities, the no-kill caviar production remains in experimental stages and, by regulatory rules, cannot be practiced on a commercial scale.

Comment by Lianne:

The financial benefits that sturgeon farmers (particularly R.A.S. farmers) would gain from using no-kill methods would be HUGE. We would be saving literally millions of dollars over the course of our business! However, even if these methods currently worked, could we honestly say we are doing it for ethical or financial reasons?

One could argue that using no-kill caviar methods is more cruel than quickly killing the fish. Although us animal lovers are attracted to the idea of not killing a magnificent animal, the reality is that no-kill methods are extremely stressful to the fish’s biological system. And unfortunately, it is very likely that the fish will end up dying from extreme body stress after these procedures. It may be more ethical to quickly kill the fish, instead of causing so much stress and pain in the name of financial gain.

Farming endangered sturgeon species is the most important factor in species conservation. Catching endangered sturgeon species in the wild is banned, with aquaculture being the only stop to the black market. All critically endangered sturgeon species are farmed. For every Russian sturgeon raised and harvested on the farm, another one takes it’s place.