Yes, the blue ones are definitely fertilisers. I have seen those being used by my mother-in-law in her garden. I am not sure of the ingredients. So, it's unknown whether it's harmful or not to the fishes. I agree with miremonster's suggestion to separate the seeds from the ferts.
Yes, customary mineralic NPK garden ferts here in Europe looks alike, the blue stuff is called "BlaukorndĂĽnger" (blue grain fertilizer) in German.
Maybe a mix for sowing lawn or meadow outdoors incl. starter ferts, so probably the content of the shipment can be used to make a nice cabbage patch bordered by grass

The longish seed looks to me like that of common temperate grasses (Festuca, Poa, Lolium etc) but I don't know what the big dark and small yellow grains are (seed?), we'll see.
I'm trying to locate some local ditches, swamps and lakes that are left somehow untouched. It's hard to find any freshwater bodies in Karachi. Our boring's and well gives brackish/saltwater. I'm thinking of organizing a small group trip to some ditches in March/April. I think spring is a good time to look for plants. No?
Surely interesting! Is there a possibility to find folks knowing the local flora, botanists or so? Favorable time: I can't really judge that for your area, it's dry period in the spring months, not? Maybe several aquatic or semi-aquatic plants are still dormant or dried, but probably still seed-bearing then. It's surely paying to have a thorough look at every green stuff, also when it looks boring at first glance, in all zones that are at least regularly flooded during the moist period.