Black-axil chromis, Blackfin chromis, Blue-green puller
The black-axil chromis (Chromis atripectoralis), also known as the blackfin chromis or blue-green puller, is a damselfish from the tropical Indo-Pacific. This fish can reach almost 12 centimetres (4.7 in) in length. It inhabits lagoons and reefs after settlement in the late-larval stage, and often occurs in large numbers, feeding above Acropora corals. This fish mostly feeds upon copepods, amphipods, and zoea.
This fish is often confused with its sibling species Chromis viridis.
C. atripectoralis is a blue-green damselfish that grows to a maximum length of twelve centimeters. The head and dorsal side of the fish is blue-green, while the belly is white to white-gray. C. atripectoralis has both an inner and an outer row of conical, widely spaced teeth.
C. atripectoralis is the sibling species of the blue-green damselfish C. viridis based on their mitochondrial genome. C. atripectoralis is often confused with C. viridis because the two species have a similar body shape and blue-green coloration. The two species can be differentiated by the color pattern of their fins. The pectoral fin axil of C. atripectoralis is black, whereas the upper base of the pectoral fin of C. viridis appears dusky due to the presence of black dots. Additionally, the two sibling species have different, but overlapping, numbers of pectoral rays. C. atripectoralis has 18-20 pectoral rays, while C. viridis has 17-19.
The range of C. atripectoralis spans the Indian and south Pacific Oceans from the east African coasts to French Polynesia, and the damselfish can also be found as far north as the Ryukyu Islands of Japan in the north Pacific. The habitat of C. atripectoralis overlaps with that of its sibling species C. viridis, although C. viridis can additionally be found in the Red Sea.
C. atripectoralis resides in coral reefs. As adults, C. atripectoralis shows a preference for branching corals, although the species can also be found in plate, sub massive, massive, encrusting, soft, and dead corals. Juveniles exhibit a preference for living in both branching and plate corals, although they have been found in sub massive corals as well. Adults may live in rubble or pavement as well, while juveniles have only been found to live in consolidated pavement. Loss of the coral reef niche is correlated with a decline in C. atripectoralis populations, as this species is highly specialized to live in reefs.
C. atripectoralis can tolerate higher water temperatures relative to cardinalfish that occupy the same habitat. C. atripectoralis does exhibit a reduction in aerobic scope across the high water temperature range of 29 °C to 33 °C; however the fish can still aerobically respire at a rate greater than half of its aerobic scope under normal conditions. The relatively high thermotolerance of C. atripectoralis may allow it to live at latitudes closer to the equator and to resist extinction as global ocean temperatures rise.
