The text below is quoted from the article 'Pipefish, Museums, Marine Naturalists and Fish Conservation'

in the Marine Life Society of South Australia 2003 Annual Journal no. 13 (Browne 2003)

The reproductive biology of the Syngnathids is particularly interesting as the males brood the eggs. Seahorses have well developed brood pouches, seadragons have brood patches, and pipefish have brood patches which are enclosed to varying degrees. The brooding of eggs by males means that acceptance of the female by the male is a limiting factor in conferring genes to the next generation. This infers that the females would be advantaged by competing for males by ornamentation, pairing, courting or aggression, and all these activities have been observed

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Courting is normal before mating in the Syngnathids, with complex courting rituals a pre-requisite to mating. In South Australia, females of both the Wide-bodied Stigmatopora nigra and Spotted pipefish court the males by displaying their chests which are barred. The chest of the Wide-bodied pipefish may be bright red. The South Australian Deep-bodied pipefish, Kaupus costatus has the greatest difference of form between males and females of any pipefish. The females are flattened sideways to display bright red and blue bars. Pairing is common in seahorses with pairs observed over long periods. However, pairing does not always mean fidelity as a wide range of mating patterns are documented in the Syngnathids, including genetic monogamy (faithful pairs) in a seahorse, and polygynandry (more than one female mate) and polyandry (more than one male mate) in pipefish (Jones and Avise 2001).

Recent studies using molecular techniques to elucidate paternity have shown that polyandry is common in some pipefish species. Moreover, in these species the intensity of sexual selection on females rivals that of any other animals (Jones et al 2001). This, and more females than males, with some females never reproducing in some species, results in very different behaviour between males and females; the males are faithful and the females are dedicated, if promiscuous, partners. Male pipefish reject courting females other than their partner, maintaining the pair bond over seasons. This fidelity, and studies showing that even in primitive pipefish where external fertilization occurs, eggs exposed on the brood patch were all fertilized by the tending male, show the evolution of enclosed brood pouches is not a response to cuckoldry by sneaker males (McCoy et al 2001).

Some have suggested that species which live amongst shelter which could brush away the eggs would have brood pouches. However, brood pouches are found in seahorses which do not violently interact with substrates, and brood patches in seadragons which have similar behaviours. Why then do advanced pipefish have a brood pouch? In these species, the embryos are attached to a placenta-like tissue which seals the pouch folds. The most apparent reason would be to reduce predation. However, no evidence exists of this. One study showed that within this enclosed pouch concentrations of salt were lower than in seawater (Watanabe et al 1999), perhaps reducing the energy expenditure from the egg needed for osmoregulation resulting in fitter larvae from similar sized eggs. If this is the case it is a further transfer of reproductive effort from the female to the male.

Mate guarding by females has been suggested as the main mechanism for maintenance of monogamy in males of pipefish; males losing their partners re-mate within a few days. Females will mate with other males besides their mate during a breeding episode (McCoy et al 2001). However, for unknown reasons widowed females remain unmated for a considerable period (Matsumoto and Yanagisawa 2001). Females in their quest to reproduce with as many males as possible have larger home ranges and are more active in  courtship displays (Matsumoto and Yanagisawa 2001). Some interesting benefits have been shown from competition for partners in the pipefish. Broods from preferred matings when either males or females were allowed to choose a partner are superior at escaping predators and grow faster (Sandvik et al, 2000).

The number of eggs in most species of pipefish is not documented. A number of males from the South Australian Museum carried eggs or had mature brood pouches. This has enabled the first tabling of the fecundity of many species. A surprising find was that most species of pipefish only had between 20-30 eggs. This is in contrast to many seahorses which lay hundreds of eggs. In the Wide-bodied pipefish, reproduction had been shown throughout the year. However, there were few species with enough specimens over the seasons to show seasonality from the South Australian records. In many other species, the presence of brood pouches showed few males and in some species no males were found. Brood pouches could be subjected to seasonal variation or these samples could include only female or juvenile pipefish. If this is the case, other un-sampled habitat may be needed for reproduction. Further knowledge will be gained on reproductive status of individuals by their dissection to show the sex and the maturity of gonads

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Although in many pipefish, hatching time and the period between batches is not known, hatching time generally varies from 10-30 days. Pipefish can have several broods in a season, with non-brooding intervals as short as a few days (Matsumoto and Yanagisawa 2001). Many species have been shown to reproduce throughout the year (Howard and Koehn 1985). However, even closely related species may vary in respect to seasonality. The most likely reason for seasonality is variation of the potential adult food and larval supply.