About Corythoichthys haematopterus (Bleeker, 1851)
Corythoichthys haematopterus, commonly known as messmate pipefish, has an elongated body with a long narrow snout, soft-rayed dorsal fin, and caudal fin. Adult messmate pipefish range in length from 9 cm to 18 cm, with an average length of 13 cm. Their coloration is variable: most have a pale body, a striped or reticulate head, poorly defined brown horizontal stripes on the sides of the trunk and tail, and a dorsal fin without pale spots. Bands are generally less visible on females, which also have dark splotches on the underside of the anterior trunk rings. Males may have bright blue transverse bars on the ventral side of the anterior trunk. Males have a brood pouch on the ventral side near the tail; instead of protective plates, the eggs are covered by fleshy folds. Juvenile messmate pipefish generally lack a color pattern, but have spiny, serrated trunk and tail ridges, and post-larval membranous dorsal fin folds that extend along the tail. Coloration becomes visible as they mature to around 4 cm, and adult ridges are mostly smooth. Messmate pipefish from the Seychelles have minimal markings across their entire body; when markings are present, they are light brown and do not follow any particular pattern. In contrast, messmate pipefish from Sri Lanka and the Pacific are well patterned, with a strongly reticulate pattern on their heads. This species can be distinguished from other members of the Corythoichthys genus by having 17 trunk rings. Messmate pipefish have approximately 48-54 total body rings, 16 pectoral fin rays, and around 29 dorsal fin rays. Messmate pipefish inhabit the Indo-Pacific region, covering tropical waters from the Indian Ocean to the Pacific Ocean. They are found in shallow seawater between 0 and 19.8 meters deep, near sandy bottoms in reef, seagrass, coral, and rocky habitats. They cannot tolerate salinity fluctuations and prefer warm temperatures. The population size and abundance of this species are unknown. Messmate pipefish are strictly monogamous. They mate with the same partner throughout the breeding season and remain paired until one dies or disappears. Despite being monogamous, females are the primary sex that competes for mates, which is a reversal of traditional sex roles where males invest more in mating and females provide most parental care. In this sex role reversal, males are typically more choosy. A male's brood pouch can only hold one clutch of eggs at a time, which prevents him from successfully mating with more than one female. Occasionally males are observed carrying two clutches, but the outer clutch cannot adhere properly and always falls off within one day. Females cannot divide their clutches between different males. Pairs mate around 8 times per breeding season, which runs from April to October. Each male's brooding period (the time between egg spawning and hatching) lasts 9 to 19 days, and higher water temperatures lead to shorter brooding periods. Females spawn eggs every 9 to 24 days. Larger females produce more eggs, as well as larger eggs; larger eggs produce larger offspring with higher anti-predatory capacity. Before breeding, a pair performs a courtship ritual including the following displays: approach, parallel swim, arch, both arch, cross, up, both up, spawning, and wiggle dance. The ritual starts at sunrise and lasts for one hour. During the "both up" display, the pair swims horizontally with their genital regions close together. The female lays eggs as a flat sheet before horizontal swimming stops, then the eggs are turned inside out and attached to the male's brood pouch. After mating is complete, the male provides all parental care, including protecting, aerating, and osmoregulating the clutch. Populations generally have more females than males, so some females do not reproduce every breeding season. Most males are paired. Unmated females may sometimes intrude on pairs performing their courtship ritual, but the male's paired female partner guards against this. Females also have a larger home range and travel further than males. While many adult individuals have overlapping home ranges, interactions with other pipefish are generally non-territorial, except on the morning of spawning, or when mated females guard their partners from other females. Even though there are more females than males in a population, males will not mate with more than one female. Males that switch mates require more time between spawning cycles, which reduces the number of breeding opportunities they have in a season. Even though larger females produce more fit offspring, males do not appear to prefer larger females. Size may still play a role in mate choice: the amount of eggs that fits in a male's brood pouch matches the size of the clutch the female can extrude. Males that are significantly smaller than their partner may not be able to hold the entire clutch.
