I reviewed the slides with our fish pathologist and their conclusion is that the white cells here are mucous cells and not adipose.
This is what likely causes pimples on the wen, extra mucous builds up and becomes a home to microorganisms occupying the crevese in the wen.
I found an interesting
zebrafish paper where the essentially made "wens" or papillomas all over the fish. There are some great pictures here:
Ethylnitrosourea (ENU)-induced hyperplasia and papillomas (gross). A, Multiple papillomas (arrows) in a fish with a total of 22 papillomas (Fish W). B, This white plaque of epidermal hyperplasia (between arrowheads) obscured the normal melanophore pattern of the zebrafish stripes (brown dot pattern, left and right) (Fish K). Epidermal hyperplasia obscured the pigment pattern, because melanophores are near the epidermal basement membrane, deep to the thickened epidermis. C, Early sessile papillomas (arrows) frequently occurred at or near the distal ends of scales (Fish I). D, Two sessile papillomas (arrowheads) on the dorsum, midline, of Fish O. E, A pigmemted pedunculated papilloma. This papilloma was 1.5 1.2 1 mm and had a narrower 0.4 0.3 0.1 mm stalk (Fish N). Cells with melanin pigment were present histologically (see Fig. 2F). Scale bars: 1 mm.
Microscopic appearance of epidermal lesions induced by ENU. A, Normal epidermis of body scales is thin and is composed of keratinocytes (k), mucous cells (m), and club cells (c). Keratinocytes (k) are squamous epithelial cells that are red, slightly smaller than club cells, and that have intercellular desmosomes. Mucous cell nuclei are pushed to one side. Mucous cells stain light blue with hematoxylin and eosin after formaldehyde fixation (shown), and deep blue after paraformaldehyde fixation (not shown). Club cells are pink, with central nuclei and occasionally scalloped edges. Scale bar:10 mm. B, Hyperplastic epidermis was thicker than normal but was composed of the same cell types as normal epidermis. Scale bar: 100 mm. C, Sessile (broad-based) papilloma composed of keratinocytes (k), mucous cells (m), and club cells (c). Scale bar: 100 mm. D, Pedunculated papilloma. All except two pedunculated papillomas were composed of keratinocytes (k), mucous cells (m), and club cells (c). Medium-sized vascular spaces were lined by a thin endothelium (arrowheads). Capillaries (*) contained red blood cells which have dark nuclei and red cytoplasm. Scale bar: 100 mm. E, Pedunculated papilloma. This is a section of the largest papilloma, which measured 8 4 4 mm, and was attached to the dorsal surface of the head between the eyes of fish H by a 0.3 0.3 0.1 mm stalk. The papilloma and eye are shown; the remainder of the body extends to the left. Histologically, keratinocytes and mucous cells, but not club cells, were arranged in solid, nested, papillary, or glandular patterns. Vascular spaces were present. Scale bar: 1 mm. F, Pigmented papilloma. This papilloma variant was composed predominantly of a uniform population of keratinocytes that flatten towards the surface and that are arranged in cords around circular areas of dense collagen and basement membrane material. Numerous melanophores account for the dark brown spotted pattern seen grossly (see Fig. 1E). Scale bar: 100 mm. G, Whorls of squamous cells (squamous eddies, arrowheads), occurred at the distal end of spiny rays of some fins. Scale bar: 100 mm. Hematoxylin and eosin.
