thesis: salinity vs. growth rate

[doughboy979]

hi fellow reefers, i'm a senior at UC Berkeley and soon to be starting my thesis for environmental science. i was wondering if any of you had any pointers for me along this line.

basically my thesis is about how salinity affects the growth rate of fishes. first of all, i would need to choose a good hardy fish to do this experiment on. i was thinking about utalizing damsels as my primary test subject. i would set up three different tanks with different salinity. one hyper, hypo and the last being a control.

i know damsel fish are hardy and can withstand a lot of stress so that's why i'm considering it as my subject. my hypothesis is that with a salinity of 0.26, the fish will grow at the maximum rate and anything above or below that would show that the situations aren't ideal.

just so that people won't hate me, no fishies will be hurt in the process cause i will return the fish back to the LFS unless someone wants them. they will be fed daily and i will be measuring their total volume to determine the growth rate.

if someone can suggest a cheaper fish or a fish that's more appropriate for this experiment, please feel free to add some input. if anyone would like to know more in detail about what my experiments are going to entail, feel free to post away =)

also, where would i be able to get an electric salinity sensors. i would like to be as accurate as possible. thanks for all your inputs.

 

[Terry B]

Interesting idea, do you plan to use just three fish? You need to elminate all possible variables such as pH, dissolved organics, temperature etc. Will you be measuring the amount of food given to each fish every day?
I have actually heard anecdotal reports that a reduced salinity can contribute to an accelerated growth rate in bony reef fish. The theory behind this is that fish expend much less energy in osmoregulation in hyposaline water, therefore more energy is available for other bodily functions such as growth. You see reef fish do not survive in highly saline water because of the salinity but despite it. I suspect the results you will see depend a great deal on exactly what salinities you use in each aquarium. I would expect the growth rate to be good in hyposaline water provided the salinity is no lower than 13ppt. If you have seen a guy named Heinrich on any of the saltwater message boards I think he told me that he actually saw better growth in an angel that he kept in hyposalinity verses another angel of the same species that he kept at NSW. I look forward to hearing more about your experiment. Wouldn't a refractometer be accurate enough?
Terry B

[ May 03, 2002: Message edited by: Terry B ]</p>

 

[Mouse]

For your information, clown fish can actually be aclimatised to live in fresh water. Not that i think this is a good practice to promote, but in light of your research i thought you may be interested.

 

[cyberpanther]

mouse so can certain damsels. My main concern is that you are only using 3 fish. What if one dies one has better genetics, then as Terry B said PH etc. You would need, in my opinion, 9 fish. 3 for each salinity. Also which damsels are you going to use some grow larger and faster than others and would be easier for a test like this. Try the dominoe damsel, it's a little aggressive and not as pretty as some other damsels but would be better for this test.

 

[Anonymous]

hi.
My hypothesis is that when a fish is living in condition that taxes it energy, it will grow slower. Salinity very different from what a fish can handle will definitely retard the growth, or even kill it. Fish expense large amount of energy in maintaining isostaticity (sp?). With that being said, it would like to point out that some fishes, as mentioned already, can live in a wider range of salinity than the others. Molly and moonfish, for examples, are blackish fish that will do well in both types of water, and I feel (depends on what you really want to prove) that they are not a good candidate for your experiment. Another variable you have to consider is the genetic variation among member of the same species. Even in the same brood, some fish grow faster than the others. You need a larger number of test cases. But then, it depends on your time and money constraint, as well as how "bullet-proof" you want your experiment to be.

 

[Len]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Terry B:
<strong>You see reef fish do not survive in highly saline water because of the salinity but despite it. I suspect the results you will see depend a great deal on exactly what salinities you use in each aquarium. I would expect the growth rate to be good in hyposaline water provided the salinity is no lower than 13ppt.</strong><hr></blockquote>

I agree with Terry's hypothesis. My estimate would be fish grow well (arguably better) in hyposaline (relative to NSW) environments down to 12-15 ppt (ionic concentration of blood). Below this, I'm not sure most marine fishes' kidneys (namely their Bowman's capsule) are capable of replacing enough ion it loses to the environment.

I should note that lower salinity levels may increase fish vitality/viability, but it also encourages growth of other organisms, worst of which are pathogens. For example, Vibrio grows well in hyposaline conditions. In other words, I wouldn't want to see everyone lowering they're s.g. after reading the previous info in this thread.

Interesting test! As suggested, make sure other variables are controlled to the best of your abilities, and analyze more subjects then 3. 3 is a very small sample size and should not accurately reflect averages. Damsels (Pomancentrids) are fine candidates since they're readily available and affordable.

Keep us posted.

 

[doughboy979]

hehe well we can only speculate on what would happen and that's why i'm doing this experiment. i will have more than 3 fish to experiment with. i will have all in all a total of 24 fish, 8 in each catagory. i'm still trying to find a suitable species for this experiment. It's every intersting to hear all your hypothesis and i have yet to do some background research into this. i won't start on my actual experiment until august so i'm trying to get all the equipment and preliminary findings out of the way right now.

in order to eliminate all the possible confounding factors, i would set up three identical tanks, running the same type of filters and using the same RO/DI water, but the salt content for each would be different. I would start off by not having any livestock in the tank. i would first make sure that the only variable between the three different tanks is the salinity and nothing else.

for the stock of fish, i would have to buy them all at once, and those within the same size. this would prevent other factors like age and such to mess up the data.

to address the concern that the damsel fish can adapt to different saline contents, i would make an analogy with humans. we are pretty adaptable to our environments, but in certain situations (lack of food, bad water, etc) one group of people would grow faster than the other. i don't know if i'm getting my point across, but i guess we can still see a varying rate of growth at different conditions such as salinity.

there are still a lot of kinks to be worked out with this experiment. i look forward to any input you guys may have and in about a year, i will be able to post my findings =)

 

[Terry B]

I wanted to bring this post back because it has been almost a year now. Has anyone heard how the experiment went?
Terry B