1. Does this fish show countershading characteristics?

Yes Dogfish show countershading characteristics from the fact that only Pelagic species can have that coloration. Pelagic is living in open oceans or seas rather than waters adjacent to land or inland waters.

2. Does this fish have any spines? Where are they located?
The dorsal fin of the spiny dogfish is somewhat larger than the second dorsal fin. Two large, sharp, mildly poisonous dorsal spines are located in front of each dorsal fin. The dogfish uses its spines defensively by curling up its body and striking at an enemy. Dogfish skin is rough and covered by a toothlike, scaled surface called dermal denticles. The skin feels smooth when rubbed with the grain of the denticles, but feels rough when rubbed against the grain.

3. Is it a male or a female? How do you know?

 The Dogfish is both male and female. The dogfish shark is unique among fish due to the fact they reproduce internally.  The parts of the dogfish shark male urogenital system include the testes, mesorchium, the efferent ductules, kidneys, mesonephric ducts, accessory mesonephric ducts, seminal vesicles, sperm sacs, urogenital sinus, cloaca, urogenital papilla.  The female dogfish sharks reproductive parts include the ovaries, mesovarium, oviducts, mesotubarium, kidneys, mesonephric ducts, urinary sinus, cloaca, and the urinary papilla. In respiration, dogfish sharks rely primarily on their gills.