Ich currently have a 60l aquarium on my cupboard which weighs approx 85 kgs. I want to upgrade to a 100 liter aquarium which will weigh approx 140 - 150 kgs and wanted to be on the safe side and ask for your opinion. Thickness of board under aquarium is 3 cm while two wooden legs are 1.5 cm. On 4 sides the main board which is under aquarium is supported by screws to main wooden pillars which are 4 cm each. . I am adding pics as well.
Properly speaking, this question can't be answered. (Unless you can find the manufacturer and ask them...)
However, I have a few ideas to offer. From a design standpoint, you have two relatively solid uprights supporting the weight. That's a good thing.
I can't really comment on the rigidity of the entire unit, but if you feel brave, remove the existing aquarium and have 2 adults climb onto where the new aquarium would be (stand over the uprights). If it felt solid, I'd assume that the structure would hold up.
If you do change the aquarium, pay special attention in the first month to see if there's any curving/bowing in the uprights, or sagging in the horizontal shelf.
If you have some heavy objects that are not valuable (such as scrap metal, anvils, large rocks, things that in the event that the desk will break will not cause much loss of money) you could try to load it in steps.
For example, load it at 100 kg for a week, while watching it structure, measuring the height in several points, looking for bowing, looking for joints starting to fail etc.
Then if this is ok move to 120 kg and further.
I would not try using people or pets as in the event of a sudden breakage they could get hurt or worse.
I don't particularly like the idea of significantly increasing the load on this piece of furniture. Sure you have two uprights directly beneath but racking and twisting are a potential concern. In addition, water ingress, from a big enough spill or even small amounts repeatedly over time, could weaken the MDF.
Far more has been asked of far worse structures and been gotten away with I'm sure, but you will want to make a risk-benefit analysis here. If you have your heart set on a heavier tank, perhaps consider replacement or at least some modification, reinforcement and/or mitigation of MDF moisture mushing. (Also, apologies all around as arbitrary alliteration apparently aggravates)