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25

The answer to this, I reckon, is that they don't. They use molecular oxygen (O2) dissolved in the water for respiration, where it acts as a terminal electron acceptor, just as we use molecular oxygen in the air for respiration. We can speak of the water as being oxygenated. Water is split in photosynthesis, where reducing equivalents from water are used ...


10

Cetaceans (i.e., marine mammals) evolved from certain ancient land based mammals, thus the tail is essentially convergent evolution of the tail function.


10

Answer The mechanism for salmon natal homing isn't exactly known, but there are really two good hypotheses out there. Salmon have an extremely good sense of smell. One hypothesis is that they retain an imprint of their birthplace's odor, and manage to recognize it again at a later time (as explained by this article). Another hypothesis: the Earth's ...


5

Intelligence is something which has to have a definition, and there are many, but I would cautiously say no. The reason that I say this is because swarming behavior can be largely reproduced by a simple set of rules - matching distance to your neighbors and direction and speed as well. To me this really removes any intention or even conscious element to ...


4

I can't answer your third, but I can answer your first two. With one word, in fact: Bioluminescence http://brightnepenthe.blogspot.com/2010/08/palate-cleanser-90.html That's the deep ocean at night for ya. Unlike underground environments and caves, it's not pitch black pretty much anywhere in the ocean. There are things to see everywhere, and they play ...


4

The mechanisms of osmoregulation is different for sharks (and other elasmobranch fishes) and teleost fishes. In Elasmobranchs the body osmolarity is maintained equal to the seawater by Na⁺ Cl⁻ and urea. Toxicity because of high concentrations of urea (strong chaotrope) is counteracted by high levels of trimethylamine oxide (TMAO). So, the elasmobranchs do ...


3

It's probably bacteria. Here's a pdf describing the phenomenon, along with an in-depth history of the reported occurrence, which should tell you everything you might want to know. These seafood products exhibited luminescence due to the presence of certain bacteria that are capable of emitting light. Luminescence by bacteria is due to a chemical ...


3

This due to a phenomenon called "cold shock". This induces a number of physiological changes in the fishs metabolism and also in its behaviour and can lead to death. The first paper cites some reasons in table 1: Brain and central nervous system response: Changes in neuronal activity Catecholamine and corticosteroid response: Release of hormones due to ...


3

I'm taking this question at face value. Yes, fish have gills, but we also have a respiratory surface in our lungs so why couldn't we 'breathe' water and extract the oxygen (since extraction is a simple matter of diffusion from the content of the lungs into the blood). Apparently we use 550 L of pure O2 per day. This works out as approximately 400 g. The ...


2

Wikipedia has some revealing information here: Not all puffers are necessarily poisonous; Takifugu oblongus, for example, is a fugu puffer that is not poisonous, and toxin level varies wildly even in fish that are. A puffer's neurotoxin is not necessarily as toxic to other animals as it is to humans, and puffers are eaten routinely by some species of ...


2

Indeed tuna are present in the Baltic sea, and they can also grow in the Pacific and Indian oceans. A lot of the tuna we see in tuna cans in supermarkets comes from the stocks in the Indian ocean, but it is possible to have fresh tuna from the Baltic. Sorry, I only found a French answer from a famous French news paper: ...


2

To add some detail to Christian H's answer, while fish tend to move from side to side (lateral undulation), the land ancestors of marine mammals had their limbs under them and so their spines were adapted to up and down movement (dorsoventral undulation). Hence, vertical tails in the former and horizontal in the latter (the wikipedia article on fins gives ...


2

I only found this two references, but these are only secondary sources at the moment. Look here "Clown Fish Anemone" and here "Choosing Clownfish and Anemones for Your Aquarium". It seems that there are only around two handful of anemones capable of supporting clownfish. Here are some primary sources which confirm the 10 anemone species: "The anemonefish ...


1

Two things to add the the answer from @Chris. We are used to the idea that fish extract oxygen from water using gills. When such a fish is transferred into air we imagine that it can no longer breathe. However fish do in fact obtain a significant proportion of their oxygen through their skin. Furthermore, as long as the gills remain moist it should be ...


1

I have been trying to find an answer to this question, but until now, no one seems to have really analyzed why this is possible. The only hint I found comes from this paper: A study of the distribution, habitat, behaviour, venom apparatus and venom of the stonefish. They state: At periods of low water, stone-fish are often left partially exposed by ...


1

When we talk about "artificial intelligence" we are talking about the ability to solve problems not directly specified in the code. It doesn't need to have "intention" or "conscience", as @shigeta suggests. So, I'd say swarms are intelligent, it's just another "hardware" where intelligence appears. Like shigeta said, our own mind is not different in essence ...


1

Sockeye salmon species definitely do, although admittedly the interesting salmon are those that spend significant time in the ocean. Here's some evidence that carp can. Raindbow trout are also capable. Zebrafish are also able. Japanese eels too, of which some are freshwater.


1

If by 'fishery' you mean "amount of fish caught", the answer is a qualified no. Sweden's catch has been stable or perhaps slightly increasing since a low in 2005, but the catch is still much lower than a decade ago (Statistics Sweden). This is presumably due in large part to the quotas set on Total Allowable Catch for various sea regions. If by 'fishery' ...


1

I believe it is mainly due to hydrodynamics. Scales reduce drag while allowing for the body to be able to still move. Drag only occurs in the back part of the fish, so there is where you need scales. Please refer to http://darwin.wcupa.edu/~biology/fish/pubs/pdf/ISSDR(drag%20reduction).pdf for other interesting biological solutions for drag reduction.



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