The object you found could either be a spine bone of a large fish or a piece of Minoan ceramic pottery. Distinguishing between the two would require an examination of the texture and material, comparing it with known biological textures or ceramic manufacturing techniques.
The object you found on the beach in La Línea de la Concepción, Spain, might indeed be a spine bone of a large fish or a piece of pottery. The 'V'-shaped mark and the 5.5 cm diameter could indicate that it's of a biological origin, especially if it has a structure similar to spine bones seen in images. However, it's also possible that the object is a fragment of a Minoan ceramic originating from pottery, known for refined clay and wheel-made techniques, similar to the elite Minoan ceramic manufacture described for vases found at Palaikastro.
Without further expert examination, it's quite difficult to determine the exact nature of your find. If it's bony in texture, it may well be a fossil or a bone fragment. If the material feels more ceramic-like, then it could be a piece of pottery, potentially influenced by the historical production techniques seen in Minoan culture.