Cannabis Science, CBD

What Happens If Fish Eat Weed?

fish swimming

Have you been curious about what happens if fish eat weed? Turn out you’re not alone. Scientists have done experiments with fish and marijuana to see what would happen. Here’s what they found. 

Photo: Unsplash 

Can Fish Get High?

We know that marijuana can affect animals, and they’ll show signs of being high or intoxicated. However, we’re not sure if fish get ‘high.’ At the same time, weed can affect fish in some way. 

2017 study examined if weed can help fish be less stressed. This study was critical because fish stress has risen due to a change to industrialized intensive systems for fish. In addition, the study highlighted that disease occurrence was increasing and wanted to find out if weed could help with that.

Therefore researchers sought to find out if cannabis oil could:

  • Improve hematological indicators of disease resistance
  • Relieve stress
  • Improve growth
  • Improve feed conversion

There were three diets for tilapia fish; soy oil, industrial hemp oil or cannabis oil. After eight weeks, the scientists noticed a few things.

The scientists noticed that weed was able to increase metabolism and feed conversion. Due to the increase in metabolism, there was a reduction in growth rate. On the other hand, weed didn’t seem to improve their immune function. The study said, “cannabis had no effect on blood cell counts, total plasma protein, haematocrit or lysozyme activity. Results thus suggest that cannabis does not improve immune response of tilapia or body composition”.

However, unfortunately, the fish weren’t getting any long-term relaxation. The study said, “Fish with hemp oil in their feeds had suppress[ed] aggressive behaviour but the effect was lost after prolonged administration.” Therefore, the hemp oil likely had a sedative effect, but the tilapia may have developed tolerance. The study concluded that there wasn’t any real benefit to giving fish cannabis oil.  

Other Studies Done With Fish and Weed

That wasn’t the only study to see what happens if fish eat weed. In 1971, scientists examined the relationship between fish, cannabis extract, and THC. Siamese fighting fish (Betta splendens), which have spontaneous, aggressive behavior, was given cannabis to see if they would calm down. The study found that cannabis did work but only for a short period. Weed was described as a “strong suppressor” of their aggressive behavior. But just like the study mentioned above, the fish developed tolerance quickly. The study said, “[H]owever, after 8–10 exposures the fishes developed tolerance to the drugs. Continuing the treatment up to 31 days did not induce any further modification in the behavior of the fishes.”

There are even more studies that examine what happens if fish eat weed.

A 2014 study that examined cannabis as food for fish had some interesting findings. The scientists examined weed, specifically the C. sativa leaf, because they found 9 Essential Amino Acids (EAA). However, fish usually need ten essential amino acids. But the study concluded that “phytochemical analysis revealed important bioactive compounds that can reduce stress conditions, boost appetite and immunity and seduce fish.” In other words, marijuana may be viable fish food. 

What About Fish and CBD?

Companies have claimed that cannabidiol (CBD) is good for fish. They claim that CBD can make fish feel less stressed. One such company claims that adding it to fish food would do the trick. However, according to Reef Builders, there isn’t enough research to justify that. They reiterate that heathy-looking fish doesn’t mean the fish is less stressed. They suggest that researchers examine cortisol levels before they make these claims. 

In addition, at least one study has looked at CBD’s relationship with fish. A 2018 study looked at what happens when zebra fish are fed CBD. The study found that the CBD caused the Zebrafish to have “significantly decreased swimming speed and swimming distance.”

In addition to that, the study found that there was “down-regulation of several other immune-related genes.”

Even though that was only one study, CBD doesn’t seem too great for fish, at least Zebrafish. 

The Relationship Between Weed and Fish Poop

Some cannabis growers are using fish poop to fertilize their cannabis plants. According to Michigan Live, Thumb Genetics is one company that facilitates this. As Michigan Live explains, after the fish expel their fecal matter, the water is filtered through a series of white PVC pipes into various pools. The water then goes into a 1,200-gallon water tank filled with red wiggler worms. The water is further refined. Eventually, the water makes its way into the grow rooms.  

Interestingly, weed and fish could benefit each other. Who knew?


What happens if fish eat weed? Well, based on the studies, they’re likely to be sedated. However, that seems to be temporary. Weed may be viable fish food based on the nutrients present. In addition to that, fish poop may be nutritious to weed plants. There needs to be more research around weed and fish, but there seems to be an interesting relationship. 


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].