Yes. It depends on the fish, some are complete carnivores, but there are some that survive only on plants, and some that will eat anything. They eat every plant from microscopic phytoplankton to large seaweed. There are far more Invertabrates that survive only on plants.

Marine herbivores are found within four groups of species in the animal kingdom — invertebrates, fish, reptiles and mammals — and include zooplankton, mollusks, the green sea turtle, the marine iguana and some fish species. Manatees and dugongs are the only herbivores among marine mammals.

Krill. Krill are small marine crustaceans, usually found in concentrations in cold arctic waters. This high protein fish food is considered to be “rich” and should be fed sparingly to fish. Available in freeze-dried flakes and pellets, this fish food is used as a supplement to a well-balanced diet.

Most saltwater fish will eat both macroalgae and microalgae. Many fish eat red, green, brown, and blue algae, but some fish prefer certain types. Most saltwater fish that are carnivores will never eat algae under any circumstances. Carnivores’ diets consist of shrimp, plankton, or tiny crustaceans.

Feeding your fish a little bit of food several times per day is closer to the way they eat in the wild than feeding them a bunch of food every 2 or 3 days. Most fish (even sharks) will only eat what they need to survive.

As far as vacation feeding is concerned, it’s generally safe to assume that most healthy (note the emphasis) fish will be fine for a few days to a week or so without eating depending on the species. Beyond that, you’ll definitely want to make some accommodation to have the fish fed—even if just every two or three days.

The short answer is NO! In the past, saltwater aquariums were thought of as being mysterious and difficult to maintain. Some aquarists fall into the trap of “it will only grow to the size of my aquarium.” This is false – tank size does not govern how large a fish will get. …

Saltwater fish can’t survive in freshwater because their bodies are highly concentrated of salt solution (too much for freshwater). Saltwater is more 1.6 pounds (0.72 kg) more buoyant than freshwater.

If we were to put a freshwater fish in salt water (or a saltwater fish in fresh water), they would fare similarly to our raisins and potatoes. The freshwater fish in salt water is now less salty than its surroundings. The surrounding water flows into their cells and they begin to swell and bloat, possibly rupturing.

Most ponds, reservoirs, and rivers across North America are freshwater. Some common freshwater fish are bluegills, carp, catfish, crappie, bass, perch, northern pike, trout, and walleye. Many kinds of fish live in the salty water of the oceans.