Cold-water organisms are rarely associated with beautiful, contrasting coloration, a multitude of colors, or neon highlights. We usually think of them as less attractively coloured animals than their tropical relatives. Fascinated with colorful guppies, “neon” or barbs we forget that also in other latitudes, far from the equator, nature has also equipped fish with a broad palette of colors. The whole world is full of colors and sometimes you just have to know how, where and when to look. A great example is our native common minnow – Phoxinus phoxinus, which belongs to the same family of fish as the hero of this article – Notropis chrosomus. This gray-olive fish takes on an ornate, darker and more contrasting mating coat during spawning. This applies especially to males, in which orange fins, blood-red lips and fin bases with white markings look fabulous on the iridescent emerald side of the body. Very few aquarists know this. Since this fish is not very eye-catching at first sight, and since it requires cool water and until recently was under strict legal protection, it was impossible to observe this species in an aquarium. Snorkeling in our waters is also not very popular.
Notropis chrosomus is a North American relative of the European minnow. This fish is placed in the genus Notropis, which has recently caused a lot of trouble to scientists working on the taxonomic classification of many other North American, minnow-like species. Due to the lack of sufficient data and the multitude of species, often extremely similar to each other, they used to put all these fish into one bag labeled- Notropis. However, recent research suggests that many more generic groups can be identified. The most closely related species to N. chrosomus are: N. bailey – Rough Shiner, N. leuciodus – Tennessee Shiner, N. nubilus – Ozark Minnow, N. rubricroceus – Saffron Shiner, N. chiliticus – Redlip Shiner, N. lutipinnis – Yellowfin Shiner, N. chlorocephalus – Greenhead Shiner.
Where do Notropis chrosomus live?
Originally, Notropis chrosomus occurred in the southeastern United States (in the upper Mobile River basin) in rivers such as: Alabama, Black Warrior, Cahaba, Conasauga, Coosa. However, it has also spread widely in other, neighboring river systems. The range of occurrence includes the state of Alabama, the northwestern state of Georgia, and the southeastern regions of Tennessee. The area lies on the border of two climate zones: tropical and subtropical, characterized by hot summers and mild winters. The climate is humid with high annual precipitation and an average annual temperature of 18°C. Snow in winter is rare, but it falls several times a year and lasts longer, especially in the foothills. Notropis chrosomus inhabits only the upper sections of rivers. These are streams with gravel and stone bedding, where the current is swift and the water is crystal clear, well-oxygenated and relatively cool even in summer. It can often be found in ponds, small lakes created by a bursting spring.
In the IUCN Red List of Threatened Species it has a category of LC – Least Concern. This species is represented by a large number of populations in different locations. The overall population size is estimated to be large. All the more so as, apart from local ones, no clear, commonly occurring factors threatening the abundance of the species are recorded.
How do Notropis chrosomus look like?
The typical coloration of this species is blue and silver stripes with red and pink flashes in between, extending from the mouth towards the tail. The females can also boast their unusual coloration, which is not common in carp fish. Mature males are distinguished by the appearance with age of beautiful, light blue, iridescent and shiny reflections covering the head, extending to the back and adorning the pectoral, ventral, dorsal and anal fins. Interestingly, during spawning the whole body of both sexes takes on a pink-purple fluorescent glow, which makes the fish look like they are glowing!
Notropis chrosomus – requirements
These fish are suitable for aquariums with a water temperature of 16-21°C. Although they can be kept up to 25°C, this usually reduces their lifespan to less than two years. It prefers moderately hard water, with a pH close to neutral – 7-7,5. This species feeds on small, aquatic crustaceans, insects, and plant matter, including algae. Notropis chrosomus catches what the water carries in its current rather than actively searching for food. Although it has been observed feeding on algae growing on stones and rocks. In breeding conditions it successfully accepts multi-ingredient dry food in the form of flakes or small granules. It is worth to use high quality protein and colour foods, alternately with those containing algae such as spirulina, chlorella or kelp algae.
Spawning in the wild
Wild fish spawn between May and July. Although divergence from this date in different locations is not ruled out. N. chrosomus is known to hybridize with N. bailey in the wild, as the species often spawn together. It takes place in places with shallow water and a gravel and stone bottom. They often use the pits or nest mounds of larger species, such as Campostoma oligolepis or Nocomis leptocephalus.
Males usually initiate spawning by circling over a selected mound or pit, actively swimming by swinging from side to side. Waving their shiny blue fins vigorously, they appear to mirror and reflect light rays to encourage females to spawn. Spawning occurs in groups and the fish are extremely agitated. The female and male swim just above the rocky bottom with their heads pointing downwards at an angle of about 45° and seem to be choosing the most suitable place to lay their eggs. Often other males quickly swim up to such a pair and in a series of short contractions, vibrating with their bodies, the eggs and milt of the spawners are released into the water. The eggs that do not get between the gravel and stones are quickly eaten by the fish. This situation often happens several times and after a short break, in slightly deeper water, the fish continue spawning.
Reproduction in an aquarium
For breeding we prepare an aquarium with cold water of suitable quality and clean bottom, without substrate or only with fine sand. A plastic tray filled to the brim with small pebbles is placed in the aquarium. We provide filtration in the form of a head filter with a sufficiently high flow rate to simulate water pull in the stream. When fish start spawning they go into a kind of reproductive frenzy. They then take on a characteristic bright pink-purple fluorescent color and are not particularly interested in what is going on outside the aquarium. Then you can observe them freely, as the presence of an aquarium hobbyist does not frighten them away at all.
The number of eggs laid is not particularly large. The larvae usually hatch after 5-8 days depending on water temperature. The free-swimming fry are initially too small to feed on freshly hatched artemia naupilius. Its first food is protozoa, nematode larvae and grated ready-made dry food. As the fry grow, we switch to food of increasing gradation. The young grow slowly and reach sexual maturity only in the second year of life. At this age fish also reach their full coloration. What is interesting, in stressful situations these fish can tone down their coloration instantly. Therefore, often at the marketplace or wholesaler’s, fish do not look particularly impressive. Only when acclimatized in the target aquarium they present their full beauty.
Notropis chrosomus is not a very common fish in our aquaria, but it has been appearing on the domestic aquarium market for over a decade. I hope that thanks to their dynamic nature, beautiful coloration and interesting mating behavior these fish will stay permanently in Polish tanks. I would especially recommend this species for single-species or biotope aquariums. In them it will be possible to observe the most natural-like behavior. However, it can be successfully introduced into a general aquarium with other sociable fish that prefer cooler water, such as cardinalfish, some barbs and zebra danio.
Katula, R., (2016), The “chrome minnow” of North America keeping and spawning the rainbow shiner (Notropis chrosomus), American Currents Vol. 41, No. 1.
Johnston, C. E., Kleiner, K. J., (1994), Reproductive behavior of the rainbow shiner (Notropis chrosomus) and the rough shiner (Notropis baileyi), nest associates of the bluehead chub (Nocomis leptocephalus) (pisces: Cyprinidae) in the Alabama river drainage, Journal of the Alabama Academy of Science, Vol. 65, No.4,