5

Thermoregulation and echolocation both depend on evolutions that occurred on land and seem to be less accessible to fish than to the ancestors of mammals. The heat capacity of water is much greater than air, so maintaining an elevated temperature in body tissues is both more difficult and less necessary. Still, some fish lineages have independently evolved ...


3

Yes there are many aquatic plant species which do not stand up in water. You need to look at the lifeform of the plants, such as introduced by Raunkiaer ( https://en.wikipedia.org/wiki/Raunki%C3%A6r_plant_life-form ) and later work by Ellenberg & Mueller-Dombois (1967). In fact, you're mixing up two different lifeforms : true aquatic plants are unable ...


2

Advantages of air breathing over gills? Keeping in mind water-breathing animals could still evolve lungs. Not being vulnerable to parasites and diseases of the gills, which are obliged to have blood supply close to the water. Able to colonise water regardless of salinity, able to survive warm water.


2

Many can breath air directly ; examples - bettas, gouramis, paradise , some catfish . No doubt others that do not come to mind .


2

Fish that live in cold water for most of the year actually have particularly strong hypoxia-tolerance adaptations, i.e. from summer heatwaves and algal blooms, compared to fish that are better oxygenated by waves and flowing rivers. Goldfish and other fish are able to rapidly change the surface area of their gills in less than a day. Carp, killifish, ...


2

The size (~2 inches), broad "quadrate" head, and long posterior abdomen leads me to believe this is a relative large larva of a Predaceous Diving Beetle (family Dytiscidae). The larvae are sometimes called "water tigers" due to their large mandibles and voracity as aquatic predators. One possible example: Dytiscus marginalis; Sources:...


1

Color is a characteristic of visible electromagnetic spectrum, see the graph here. Electromagnetic means here that it has the same nature as radio-waves, X-rays, and gamma radiation, whereas visible refers to the region of spectrum - waves of frequencies ranging from TeraHertz to PetaHerz (i.e., from $10^{12}$ Hz to $10^{15}$ Hz). Specific colors essentially ...


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