Were they developed anew or a heritage from fish?
According to the University of California Museum of Paleontology, similarities between pangolin and armadillos are the results of convergent evolution. So the pangolin scales are a new feature that arose somewhere on the lineage leading to pangolins.
The pangolin scale is a horny derivative of the epidermis. It is complex in structure and is divisible into three distinct regions. The dorsal plate forms approximately one-sixth of the scale thickness. It is composed of flattened solid keratinized cells without basophilic nuclear remnants. This region tends to fray easily. The dorsal plate contains bound phospholipids and sulphydryl groups but is weak in disulphide bonds. (On the nature of the horny scales of the pangolin)
It is suggested on the basis of histological structure and dishribution of chemical constituents that pangolin scales are probably homologous with primate nails.
Sorry, I forgot the second part of your question - were they developed from fish. The article suggests that they did NOT evolve from reptile scales. Since fish are even farther removed from reptiles on the evolutionary scale, I think that pretty much answers your question; pangolin scales do not share a common origin with fish scales.