2 Oct 2009

Fishy Fridays ep. 3

Oops! Fishy Friday is a week late, sorry! The "real world" (and a nasty cold) got in the way of this coming out on time... will try to keep it from happening again, but things are kind of crazy now so no guarantees! :p

So, back to business! Where did we leave off last time? Oh yeah, fish in a tank! :p


Damn! Will you guys stop swimming around so I can get a decent shot?!


Much better, thx!

Whew, taking pictures without flash in a dark space with moving objects: NOT EASY!

Why no flash you might ask? One of the cardinal rules of visiting an aquarium, to be obeyed at all times! Do you remember the scene in Finding Nemo when Nemo gets fishnapped? Right at that moment one of the divers takes a picture of Marlin, his dad. *Flash* and all Marlin can see for the next few seconds are stars... Well, fish don't have eyelids... so flash (which we instinctively close our eyes to avoid) is a big NO-NO!

Hmmm... so much movement, so many critters. Who should we start with?...



How about a fishy fellow with a ferocious name?! A WOLF! Ok, maybe not that ferocious... he's just called a wolf in French and only in the Mediterranean (Loup). In the North Sea they call him a Bar. You guys might know him as a Sea Bass, Dicentrarchus labrax. And then you probably start going Yum!


Do you remember me mentioning the Romans and fish-farming last week? Well this was another other top species in their early aquatic husbandry, so another fishy fellow we've been eating for well over 2000 years now although he's much more abundant in the North Sea than in the Mediterranean.

Hmm... they seem to have some interesting tank-mates swimming around there. Should we take a closer look? ;o)


*Jaws theme*


tah-dah!

not so scary huh? damn, I'm striking out today with the fear factor... :s

well, they're still sharks!

see:


gill slits!

which is how you ID a shark (not the funky body shape, pointy snout or the dorsal fin)

Since I'm still feeling a bit fuzzy-brained due to this damn cold... I'll leave the explanation of why sharks have gill slits instead of a bony covering for the next (bigger) shark chapter down the road... I'll give you a hint: it has to do with their skeletal structure. ;o)

Hehe, I have a very good friend here who loves these fellahs, thinks them quite cuddly in fact! And when I see them from this angle I almost agree with her:


Damn! I could have sworn I actually had a pic of her cuddling a dogfish before she collected samples (she did her PhD thesis on shark toxicology, studying the heavy metal content in individuals she fished in the North Sea), but it appears to be missing... along with 6 months worth of photos from 2004!!! grrr... methinks they might be backed up on a cd somewhere in a box back in Spain. Must make mental note to locate that! I hate losing pix...

Back to our sharks. Yeah, yeah, I know, not the "big scary" variety, but hey don't hurt their feelings, our dogfish are still SHARKS! Two different species in fact. :p


The larger ones are Scyliorhinus stellaris or Greater-spotted dogfish, while the smaller ones are Scyliorhinus canicula or Lesser-spotted dogfish (sometimes also known as catsharks). They share a similar distribution, range and diet, and here's the distribution map (from Fishbase) for the smaller of the two:


As you can see they're found virtually in all the European coastal waters, and they're one of the top species of shark caught by the fisheries. For those of you wondering why some of these guys appear to be lazing around in the bottom of the aquarium, not to worry! That's a perfectly natural behaviour for them since they're bottom-dwelling sharks (can be found between 10-400m depth) where they spend most of their time snoozing, mating (more on that below) or eating molluscs and crustaceans (and whatever they come across that a fishing boat has decided it doesn't want and tossed back in the sea). We eat them either fresh or salt-dried. I might have to try some next time I'm at the Belgian coast...

Missing from this aquarium:


R.I.P. our flat-bodied friend. Your elegant dancing is sorely missed.


The single ray we had - a "raie bouclée" or Maiden ray Rajus clavata - died last year... the fact that she hasn't been replaced yet (rays are always a big crowd favourite) gives you an idea how simple it isn't to get fish for Aquaria. You can't just go and get them anywhere... sometimes they buy wild captures, but mostly they exchange or purchase individuals from other institutions with successful reproductive populations...

Digging up one of those little videos from that tour I gave 3 years ago, here's a small Q&A on the ray:

video

Oh, and speaking of shark eggs... those spotted dogfish we've got in the tank? Well they breed like rabbits! Besides the ones you can see in the images... there are dozens more in the reserve tanks! Definitely no problems in adapting to life in an Aquarium! We used to not take all the eggs out of the tank to let the ray enjoy a little caviare now and then and help keep our population down... (and this overpopulation of dogfish is a problem of most European aquariums! My boss has jokingly discussed opening up a cafeteria and having grilled dogfish on the menu! It's supposed to be quite good...)

Two species of dogfish, two sizes of eggs. Guess whose are whose?


The dogfish are so at ease with life in the tank and not at all shy... so quite a few visitors have had the chance to see them in "action"! You can get some quite salty remarks from groups of senior citizens... or looks of shock from 9 year-olds who think they're witnessing one shark "attacking" another! Ooops! I end up looking at their teachers while trying to carefully choose my words while I explain what's really happening. And it is quite a violent spectacle! The male bites the female behind the neck and she's thrashing about while he tries to finish immobilizing her by wrapping the rest of his body around hers until he finds the necessary position to... am I getting too pornographic here? :p

Ok, let me put it this way, sharks are different from other fish in that they reproduce by internal fertilisation (so like mammals) while the other fish reproduce by external fertilisation. In order to do this sharks need a copulatory organ... i.e. a PENIS!!! OOPS! I said it!!! Oh well, the kids usually say it waaaay ahead of me, giggling their heads off while they're at it. Hey I'm a Biologist and I'm talking Biology here!

Where was I? Oh yes, so the male dogfish "gets into position", and has to hold it long enough to be sure he has fertilised all the eggs inside the female (other sharks don't lay eggs but have live births, more on that on the next shark episode). So this is about... 45... MINUTES!!!

Looks of surprise/glee/mischievous from my older aquarium visitors now. Lots of nudging between couples, and the usual wise-ass cracking a bad joke!

Once finished he heads off, his job done. And then it's up to the female to do all the work... she starts laying eggs a short while later and keeps it up 'till they're all done, a few months later!

The embryos spend 9 months in those eggs (image below, from the Muséum National d'Histoire Naturel in France), so it's important that the female find a good, safe place to put them. Preferably not directly on the seabed where they'd be smothered by sediment or gobbled up by a crab etc.


I spent hours last week poring over the internet looking for videos of dogfish reproductive behaviour to illustrate all this... but sadly I couldn't find any. :o(

Here's what I did find and that might interest you:

Someone filmed the dogfish in their local Aquarium, good view of the eggs and young sharks (very quiet):


What do you know? I just found one!!!


I also came across an excellent clip on the Discovery Channel website about shark reproduction, but sadly can't embed it, so if you're interested just click here.

Ok, I believe that's it for today! Whew! This one took me a bit longer to put together, I hope you enjoyed! Remember, if you ever want to join in on Fishy Friday just let me know and I'll link up! I still have to find the time to design some kind of fishy logo... I don't draw very well (and I don't have a scanner anyways) and I don't have any drawing software so I'll have to improvise something with PowerPoint when I get the chance...

Have a good weekend everyone!

Edit: I've got pix and video of embryo in eggs from the Liège Aquarium HERE!

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