CichlidFish.com - Fish That Think.

Paternal instinct evolution has resulted in vary ways of fry protection (mouth brooders, pit diggers etc)

Paternal instinct

Reproduction of Bitterling is unusual, involving a symbiotic relationship with various species of freshwater mussels from the families Unionidae and Margaritiferidae (Smith and others, 2004). During the spawning season, the brightly colored males defend territories around mussels. Gravid females use their elongate ovipositor to deposit their eggs into the mantle cavity of the mussel. Male Bitterling then fertilize the eggs inside the mussel by shedding their sperm over the inhalant aperture of the mussel so that water entering the mussel carries the sperm to the eggs (Smith, 1985; Smith and others, 2004). Sterba (1973) reported that females condition the mussels to the stimulus by repeatedly nudging them with their mouth, thus ensuring against closing of the valves during the insertion of the ovipositor. The same female may use a number of mussels, and she deposits only one or two yellow, oval eggs into each (Seeley 1886; Axlerod and Schultz, 1955). The ovipositor is only present during the spawning season, after which it gradually shortens until reduced to a papilla (Seeley 1886; Sterba, 1973). Smith (1985) reported that the ovipositor of one female shrank to one-third of its maximum length within 3 days after spawning. Breder (1933) demonstrated that the Bitterling could use freshwater mussels native to the U.S. for reproduction (for example, Elliptio complanata and Pyganodon [formerly Anadonta] cataracta). Contrary to what was previously thought, there is evidence indicating the Bitterling is selective about which mussel species are used for spawning (Smith and others, 2004).

      Fecundity of the Bitterling is low compared to cyprinids that broadcast their eggs. A fecundity of only 31-53 eggs per female was reported in the population inhabiting the Bronx River, New York (Schmidt and McGurk, 1982). Zhul’kov and Nikiforov (1988) reported a fecundity of 203-408 eggs per female in a Russian river. Aldridge (1999) studied an introduced population of Bitterling in Britain, and documented the large size of the eggs