My father was a seafood wholesaler at the Fulton Fish Market, and I encountered all kinds of fish at the dinner table as a child and from working in his stall one summer. I knew about halibut, redfish, flounder and crayfish, and this gefilte fish was a mix of carp, whiting and pike. My dad was even into turtles, and he would send random mystery species to the American Museum of Natural History in the suburbs to identify them.
But a few years ago, I was pleasantly surprised when large bags of shrunken tilapia fillets started appearing in the supermarket.
What is tilapia?
I like it because its softness doesn’t smell like my fishy childhood. I especially wondered what it was when I read about two high school students who used DNA fingerprinting to identify mislabeled fish in New York City sushi restaurants and seafood markets and discovered that the expensive albacore tuna was Mozambican tilapia.
So when foul-mouthed tilapia started appearing on Facebook warning against the evils of fish farming, I finally googled it – and quickly discovered that tilapia are evolutionary rock stars, and I had indeed heard of them. They are cichlid fish! Any bionerd will instantly recognize its place in natural history.
So I pulled out the introductory biology textbook that launched my writing career, and sure enough, there were the famous cichlids.
From African lakes to aquaculture
Both within and between the African Great Lakes, geological activity and time over hundreds of thousands of years have separated cichlid populations, allowing genetic variation to accumulate and persist. That’s what evolution is all about – natural selection favoring traits that make survival easier.
I wrote in my introductory biology textbook:
Their speciation in Cameroon is probably the result of ecological isolation. Some populations feed exclusively on the bottom of the lake, while others prefer areas near the roots of aquatic plants or closer to the surface. Since members of each population do not come into contact, gene exchange does not occur. As variation in the genes of each population accumulates, they become more reproductively isolated. Over many years, populations have evolved into distinct species.
Cichlids also split into new species when they split into different water bodies. I wrote “As new lakes formed, they isolated fish populations, and the animals eventually accumulated enough genetic variation to create new species. Based on comparisons of mitochondrial DNA sequences, the estimated times at which the DNA sequences diverged (calculated from mutation rates) coincide with geographic evidence of earthquakes. “Earthquakes may have created lakes that separated ancient gene pools of cichlid fish.”
About 1,650 species of cichlid fish are known, with probably 2,000 to 3,000 in existence. The number of tilapia species is about 70.
The scientific literature on famous cichlids is extensive. I was excited to find Sympathetic Speciation Suggested by Monophyly of Crater Lake Cichlids because one of the trio of authors is Swedish evolutionary biologist Svante Päabo of Neanderthal fame. It’s from 1994, but the paper trail goes back to at least 1972.
Dr. Pääbo and his colleagues described two small crater lakes in Cameroon that are not fed by rivers or streams. One lake, Barombi Mbo, has 11 species of fish, while another lake, Bermin, has 9 species, all of which are “tilapiines” or “tilapia-like cichlids”. The researchers compared 340 bases of mitochondrial DNA sequences between the 20 species, revealing that each lake has a monophyletic collection: from a single origin, each lake was colonized only once.
Attempts to expand tilapia began in the 1980s. In 1987, the Genetically Improved Farmed Tilapia project began with eight founder populations of African and Asian tilapia. “The GIFT population underwent intensive artificial selection,” wrote a team of researchers from China and Singapore who sequenced the genomes of 47 “tilapia individuals.” Nature In 2015.
The researchers examined the genomes for sequence subtleties that reflect the artificial selection (selective breeding) behind the fish’s “genetically improved” status. The list of dozens of genes showing differential changes is divided into three broad functions: reproduction, growth and development; immunity; and response to chemicals and other forms of stress.
Fish to fear?
Are the cichlids from the 1994 paper the same species as the cichlids I pulled from my freezer at Wal-Mart? Probably because the names in the Wikipedia entry for “aquaculture for tilapia” actually match the three species in the 1994 paper.
Tilapia is ideal for fish farms for several reasons:
- They reproduce, develop and grow rapidly, reaching marketable size in 7 months.
- They are omnivores, feeding on cheap vegetables and algae.
- Crowding doesn’t bother them.
- They thrive in salt, fresh or brackish water.
They are so well adapted to aquaculture that there is no need for genetic modification, although this has been done. Going GM just complicates things because the fish has to be infinite. I can say that it is simply not necessary. Sometimes nature cannot be improved.
But there are still bits of panic. The meme that caught my attention first is fueling:
“Stop eating that fake ass! This fish is boneless, skinless and cannot be overcooked. You will not find tilapia in the wild. Harvest (sic) is carried out in artificial fisheries. … eating tilapia is worse than eating bacon or hamburger. … This fish is a mutant: it is killing our families.”
The claim of bonelessness and skinlessness can be derived from this statement from Wikipedia: “Whole tilapia can be filleted, skinless, boneless.”
As for fish farms, rumors and reports claim that tilapia farms in China use manure from various sources, mainly pigs and geese. This Snopes report is particularly sickening.
Despite the fertilizer issue, I love tilapia because it’s nutritious and I’ve had a childhood aversion to fish.
Not only were my sister and I often fed disgusting seafood, we even kept two giant lobsters as pets in the bathroom until we came home from school one day to find our otherwise kind mother had killed them in a pot of boiling water. I will not eat cancer because of this trauma. I also have bad memories of fish sticks – no one knew what they were. But when I see bags of tilapia fillets at Wal-Mart, packed with protein and enough to serve about 20 kids for about $12, I can’t help but appreciate the delicate boneless and skinless white fish from Africa’s famous lakes. .
Ricki Lewis is a senior contributing writer for GLP focusing on gene therapy and gene editing. He holds a PhD in genetics and is a genetic counselor, science writer, and author of The Forever Fix: Gene Therapy and the Saved, the only popular book on gene therapy. BIO. Follow him on his website or on Twitter @rickilewis
A version of this article originally appeared on the PLOS Blog “Tilapia: Strange Farmed Fish or Evolutionary Rockstar?” and reprinted here with permission.
This article previously appeared in GLP on September 12, 2018.