I was shocked as a kid seeing tuna in an aquarium up close and realizing how big they were. The aquarium kept them in the same tank as the sharks and honestly, I was more intimidated by them than the sharks.
There are species of tuna that can reach up to 4.5m. But most canned tuna is Skipjack or Albacore and they can "only" get up to 0.8m (skipjack) and 1m (albacore).
Still pretty big though. But the huge ones are mostly sold at auction for sushi afaik
I had to look it up - only a couple of aquariums in the world have bluefin (the largest species) in captivity, most that keep tuna have yellowfin and skipjack, large fish but not nearly as big as bluefin.
I think I never saw life tuna, but I still remember the scenes from 'The Outsiders of Uskoken Castle' as a kid
(the book/TV series is also known as 'Red Zora')
There are risks of disease and parasites from eating mammalian predators that are not a risk with fish.
Predators are also a lot more expensive to raise as domestic animals. Pigs are omnivores, and chickens will eat some small animals. We feed them what is cheap. Animal feeds do sometimes contain waste meat or fish.
People do eat reptilian predators. I have eaten crocodile and monitor lizard, a number of others are eaten.
There is a lot of phytoplankton, plant-like algae. Though apparently most fish don't eat it directly. Zooplankton (which consumes phytoplankton) seems to be a more common food source for fish. You could call a fish eating zooplankton a "predator" because zooplankton are non-plant microorganisms, but that stretches the definition.
Anyway, tuna don't just eat zooplankton, they eat smaller fish. And most fish are definitely not predators of this kind, because that would be mathematically impossible.
If you are counting individual fish (independent of size) and you count all sea creatures, I think this is false. The "vegetation" are small creatures like phytoplankton, and the fish that eat them probably vastly outnumber the fish that eat fish. Each stage of the food change contains about an order of magnitude less fish than the level below.
Most small fish eat small crustaceans and other small animals, not algae.
Most phytoplankton, i.e. unicellular algae, is eaten by zooplankton, i.e. mostly by small crustaceans, like copepods.
The fish that eat other animals vastly outnumber the fish that eat algae or aquatic plants.
In open water environments, the kinds of bigger animals, i.e. fish, cephalopods, chaetognaths, cnidarians, ctenophores are almost all predators who, unless they eat each other, they are eating zooplankton that consists mostly of small crustaceans and of planktonic larvae of the animals that live on the bottom.
> The fish that eat other animals vastly outnumber the fish that eat algae or aquatic plants.
This is why I said "if you count all sea creatures". The original comment said "most fish are predators because there isn't much vegetation". As you say, there is quite a lot of vegetation, and there are many more sea creatures in that category than there are predators.
So, most fish are predators, but not at all for the reason in the original comment. It remains true that population and total biomass drop off exponentially as you go up in the food chain (which is really the only point I was trying to make).
The main reason while the majority of big aquatic animals are eating other animals, while the majority of the big terrestrial animals are eating plants, is the disparity in size between big animals and most aquatic primary producers, which requires at least one intermediate layer of small animals, who gather efficiently the small algae, packaging the nutrients and energy into bigger bodies, which can be gathered efficiently by the big animals.
The multicellular algae have bodies with a poor content of nutrients, because unlike terrestrial plants they do not need to store large reserves of nutrients in body parts like seeds or roots modified for storage, reserves that would be needed sometime in the future, after finding a place to germinate or after an unfavorable season passes. The stems of multicellular algae typically have only the purpose to anchor them to the bottom, to avoid being swept away by currents, so they do not need to contain much edible substance.
So only a few animals, e.g. sea urchins and some snails or chitons and few fish, have developed the special adaptations required to graze multicellular algae, like adequate teeth, because the reward for such an adaptation is not great and the places with abundant multicellular algae are typically restricted to regions close to shores.
Still pretty big though. But the huge ones are mostly sold at auction for sushi afaik
https://www.pnas.org/doi/10.1073/pnas.2512066123
Predators are also a lot more expensive to raise as domestic animals. Pigs are omnivores, and chickens will eat some small animals. We feed them what is cheap. Animal feeds do sometimes contain waste meat or fish.
People do eat reptilian predators. I have eaten crocodile and monitor lizard, a number of others are eaten.
Anyway, tuna don't just eat zooplankton, they eat smaller fish. And most fish are definitely not predators of this kind, because that would be mathematically impossible.
Most phytoplankton, i.e. unicellular algae, is eaten by zooplankton, i.e. mostly by small crustaceans, like copepods.
The fish that eat other animals vastly outnumber the fish that eat algae or aquatic plants.
In open water environments, the kinds of bigger animals, i.e. fish, cephalopods, chaetognaths, cnidarians, ctenophores are almost all predators who, unless they eat each other, they are eating zooplankton that consists mostly of small crustaceans and of planktonic larvae of the animals that live on the bottom.
> The fish that eat other animals vastly outnumber the fish that eat algae or aquatic plants.
This is why I said "if you count all sea creatures". The original comment said "most fish are predators because there isn't much vegetation". As you say, there is quite a lot of vegetation, and there are many more sea creatures in that category than there are predators.
So, most fish are predators, but not at all for the reason in the original comment. It remains true that population and total biomass drop off exponentially as you go up in the food chain (which is really the only point I was trying to make).
The main reason while the majority of big aquatic animals are eating other animals, while the majority of the big terrestrial animals are eating plants, is the disparity in size between big animals and most aquatic primary producers, which requires at least one intermediate layer of small animals, who gather efficiently the small algae, packaging the nutrients and energy into bigger bodies, which can be gathered efficiently by the big animals.
The multicellular algae have bodies with a poor content of nutrients, because unlike terrestrial plants they do not need to store large reserves of nutrients in body parts like seeds or roots modified for storage, reserves that would be needed sometime in the future, after finding a place to germinate or after an unfavorable season passes. The stems of multicellular algae typically have only the purpose to anchor them to the bottom, to avoid being swept away by currents, so they do not need to contain much edible substance.
So only a few animals, e.g. sea urchins and some snails or chitons and few fish, have developed the special adaptations required to graze multicellular algae, like adequate teeth, because the reward for such an adaptation is not great and the places with abundant multicellular algae are typically restricted to regions close to shores.