Serge

My tips: forget about flash, depending how fast fishy objects are adjust shutter speed to freeze their movement, avoid dark areas of the aquarium. I'd go for S mode (around 1/200 sec.) and Auto ISO. If your lens is not very sharp wide open go for M, f/2.5, 1/200 sec, ISO setting depending on light conditions and 3D tracking AF if there will be no reflections on the aquarium glass. CPL filter would be ideal but will step down your exposure.

35 f/1.8 is not a portrait lens but you can use it as it's fast. 105 and 85 mm will be to narrow for bigger objects.

Thanks UntamedSpirit

Here is another one taken that night:

Cheers,

Serge

I love 1st one - well done!

f/16 - this is the answer to your detail loss. Lenses are usually the best at f/8 - f/11max  - further stepping down decreases IQ. In general only macro lenses are designed for small apertures. Use A program, ISO 100 and set your camera to f/8 - you will see the difference.

Hello! I know it's been a while but I'm really busy Here is my one taken yesterday. Location: Isle of Sheppey, Kent, UK

D610 + Nikkor 18-35 @f/9, ISO 1000, 25 sec exposure.

Cheers,

Serge