Do larval fish have kidneys? Question about osmoregulation

[ichthyogeek]

I just got back from a very interesting thread in the reef chemistry forum. Somebody asked about keeping fish at lower salinities in order to stress them less. Someone else replied that fish have internal SG of 1.008. My first question, is if larval fish have kidneys. If not, then wouldn't it be more suitable to have them in a lower salinity environment (say 1.018 rather than 1.026) to put less stress on the fish, allow for higher gas concentration (i.e. oxygen), and allow for larger levels of copepods/microalgae to be in the water? [I have the strange assumption the larval fish would just pop...]

 

[Dkuhlmann]

If you always remember the values of natural sea water you will usually get your answer. So in this case no, there isn't any good reason to lower the sg less than that of natural sea water.

 

[HowManyClowns]

I keep my salinity at 1.018 - 1.020 in larval tanks and have had good success at those levels.

 

[shifty51008]

No reason to go lower than 1.018. I keep mine at 1.021 just so its a little lower than the dt and also at a good sg for the rotifers. Easier to keep all the breeding, and rotifer tanks at the same sg so i dont have alot of diff containers mixing sw at a bunch of diff levels

 

[ThRoewer]

Larva must have rudimentary kidneys to osmoregulate.
I kept my past broodstock pairs at 1.018 (give or take a bit) and had good success with that. I actually found that the hatching clownfish larva were larger so that they could eat freshly hatched brine shrimp from day one. They also showed a faster growth and took frozen food (Cyclops) after 4 to 6 days.

Lowering the salinity saves energy from osmoregulation that can be invested into growth and development.

 

[KafudaFish]

They osmoregulate through their skin and gill tissue among other methods depending on species.