Reproductive strategies and early development of three freshwater gobies

Three species of gobiid fish inhabit the freshwater Lake Trichonis of western Greece. Two of these species, Economidichthys pygmaeus and E. trichonis are endemic, and the third is the widespread Knipowitschia caucasica . There are habitat separations between the three species, E. pygmaeus and E. trichonis prefer vegetated areas, the first being fully demersal at all stages of development and the second being semi‐demersal. Knipowitschia caucasica prefers sandy bottoms and is distributed in shallower waters. Female E. pygmaeus and E. trichonis spawn in nests prepared by the males in the cavities of broken reeds. The males subsequently guard the eggs until they hatch, with females playing no role in parental care. Economidichthys trichonis is probably the smallest freshwater European species. Its eggs are ovoid, measuring about 0.64 × 0.58 mm, from which tiny, unpigmented and incompletely developed pelagic larvae hatch out after an incubation period lasting less than 1 day at a water temperature of 19.5° C. The eggs of E. pygmaeus are cylindrical and larger, measuring about 2.38 × 0.89 mm, from which relatively large, strongly pigmented and ontogenetically more advanced larvae hatch out after a longer incubation period. Both species reproduce only once in their lifetime, at the age of 1 year, and die shortly after spawning, but the breeding season involves several spawnings by each individual fish. These biological, developmental and reproductive characteristics are discussed in relation to current theories on evolution of life‐historics.