Common name: Royal Panaque, Royal Plec Tropical Fish
L-Numbers: L027a, L027b, L027c, possibly others
Scientific name: Panaque nigrolineatus
Origin: South America (Brazil, Colombia, Venezuela)
Water chemistry: Ideally around neutral, but adaptable
Maximum size: Potentially up to 40 cm, but usually much smaller
Minimum Tank Size: Adults will need at least a 90 cm tank
Care: Royal plecs are not quite as tough as common plecs, but they are still relatively hardy and adaptable tropical fish fish. The critical stage is buying and acclimating a new specimen to your aquarium. Newly imported specimens are often significantly underweight, and some specimens fail to recover and eventually die, regardless of the care lavished on them by the aquarist. Specimens likely beyond hope will have sunken eyes and hollow bellies. Most however will quickly regain condition if kept in a quiet aquarium (preferably a quarantine tank) and fed plenty of vegetables, wood, and occasionally supplements of meaty foods such as bloodworms. (Note that royal plecs should not be regularly fed meaty foods; see Comments below.)
Royal plecs can be kept in a range of water conditions from soft and acidic through to hard and alkaline. My specimen lived for seven years in a mbuna tank where pH and hardness were both very high, and is currently in a soft water aquarium where the pH is around 6 and there is very little hardness at all. I have seen a specimen in a tropical store kept in slightly brackish water (SG 1.002) along with scats and monos, but personally wouldn't recommend it; but this does show how adaptable these fish can be, once they are healthy and feeding well.
These fish are nocturnal, and adults are often even more retiring that juveniles. It may take months for a fish to settle in sufficiently that it will come out by day. My specimen will feed during the day, particularly if offered a few catfish pellets or a slice of courgette.
Social Behaviour: Like most of the larger plecs, these fish are territorial. They will sometimes coexist happily enough with smaller loricariids, such as Ancistrus, provided there is plenty of room and the fish do not need to fight over resting sites. Otherwise these fish are completely peaceful and will ignore any fish that leaves them alone. They are perfectly capable of looking after themselves, and will respond to bullying by cichlids in kind, but in such aquaria are likely to become very shy and retiring.
Feeding: These tropical fish need to be fed primarily on vegetables, algae, and bogwood. Among the vegetables readily accepted are carrot, courgette (zucchini), cucumber, lettuce leaves (blanched), peas (cooked), and spinach. Standard plec algae wafers and pellets will be taken as well. Bogwood is a critical component of the diet of these tropical fish. These fish eat the wood and actually digest it (most other plecs simply need the wood as a source of dietary fibre).
Planted Aquaria: Strangely, Royal plecs generally ignore soft-leaved plants but can, and probably will, damage plants with stiff stems or hard leaves. In my aquaria, my royal plec does not damage (except accidentally uprooting) Cabomba, water lilies, Hydrocotyle, and Vallisneria, for example. On the other hand, the stems of Hygrophila stricta, Rotala indica, and Bacopa monnieri are sometimes nibbled on, and the leaves of various Echinodorus species are simply grazed down to the stem. Isolated stems of hairgrass are swum through, breaking them in two, but bunches of hairgrass seem to survive.
Sexing: Both male and female fish develop bristles (odontodes) on the cheeks and pectoral fins, so these are an unreliable character for sex determination. It is believed that sexually mature males have longer bristles. Otherwise, males and females are identical.
Breeding: In the wild, the females lay their eggs in nests underneath nocks in fast-flowing streams. Fishermen in their native habitat recognise that royal plecs tropical fish move to streams with rocks substrates. Females produce around 600 relatively large (2-3 mm), bright yellow eggs. These fish have spawned only very rarely in aquaria, and details are lacking.
Growth is slow. Scientists have optimised growth rate by carrying out large water changes every few days. These fish are long-lived; my specimen is around 11 years old and still only half grown, being around 15 cm long.
Comments: A common mistake made with these fish is to feed them mussels, prawns, and other meaty foods. They do not need them. The basis of the diet must be wood and vegetables, which is what they eat in the wild. Moreover, meaty foods were believed to cause fat deposits around the internal organs found by a scientist working on Panaque catfish. Vegetable proteins (soy, algae, etc.) are a much safer option. Meaty foods like bloodworms can make useful treats or to fatten up newly imported specimens, but should not otherwise be an important part of the diet of these tropical fish.