This article originally appeared in SeaScopeTM, Volume 8, Winter 1991, Aquarium Systems, copyright 1991. All rights reserved by Aquarium Systems, Mentor, Ohio. Permission to reproduce is granted by the publisher to The Breeder's Registry and is not transferrable.
By: Stephen D. Walker
Curator of Aquaria
The Atlantic Spadefish Chaetodipterus faber is the only Caribbean representative of the batfish family Ephippidae. It is reported to reach a length of one meter (m) and a weight of 9 kilograms (kg), but any individual over 45 centimeter (cm) is exceptional. Spadefish resemble angelfish (Pomacanthidae), to which they are related. Spadefish are usually found in large schools, and will feed on practically anything. It has been proposed that the young mimic floating debris to escape predation.
The Tulsa Zoo has maintained Atlantic Spadefish on a nearly continuous basis since March of 1980. Presently we have 5 adult individuals ranging in size from 23 cm to 30 cm standard length. Three of these were received in May of 1984 and two were received in February of 1985. The sexes of Spadefish are indistinguishable, and we are, therefore, unable to ascertain the gender of each specimen.
Atlantic Spadefish egg (round) and Striped Parrotfish, Scarus croicensis, egg approximately 18 hours after spawning. Magnification is 40X. (Photo by: Stephen D. Walker) |
Our adult Spadefish are housed in a 40,000-liter exhibit aquarium featuring the fishes of Caribbean coral reefs. This tank resembles a widened "U" in shape and is approximately 9.5 m long, 2.5 m wide, and 2.5 m deep. Synthetic seawater (Instant Ocean) is used in this aquarium at a specific gravity between 1.020 and 1.022. Temperature varies with the season from 20 C during the winter to 27 C in the summer.
Observations of coral reef fish spawning patterns in the wild have suggested that many species which produce pelagic eggs spawn at dusk (Johannes, 1978 (1); Lobel, 1978(2)). We, therefore, set out to create a dusk-like condition in hopes of stimulating reproduction. The display aquarium has two lighting circuits. The main circuit has six 400 watt metal halide fixtures, augmented by twelve secondary 150 watt incandescent spotlights. The two lighting circuits are controlled separately by adjustable timers. To simulate dawn and dusk the incandescent lights are set to switch on thirty minutes before the metal halides, and to turn off thirty minutes after the metal halides have been extinguished.
Since spawning occurs in the evening after working hours, a system of sampling the water column for pelagic eggs is needed. After several trials, a simple egg collector was devised that consists of a submersible water pump of 200 gallons per hour capacity with a sponge filter fitted to the intake port. The collector is set in the late afternoon and allowed to run overnight. This has proven to be very effective and has resulted in capturing eggs from four species of fish. By comparing the features of these eggs with published reports (Thresher,1984 (3)) it was determined that three of the four species are the Striped parrotfish Scarus croicensis, the Cherub Pygmy angelfish Centropyge argi, and the Spadefish. A fourth egg type is yet to be identified. Repeated sampling of the aquarium has indicated that all species spawn daily with some fluctuation in the quantity of eggs collected from each species. The number of Spadefish eggs collected in an overnight catch varies from two to over 200, but this variation may be an artifact of the collection method and not an indication of actual Spadefish fecundity.
Once the eggs have been collected they are processed for hatching. The sponge filter is removed from the pump and submerged in a container of water from the display. It is washed to relieve it of the eggs, which are then screened through a 45 micron filter, placed in a petri dish, and viewed through a dissecting microscope.
Spadefish eggs are spherical with a single oil droplet, and measure between 1 millimeter (mm) and 1.2 mm in diameter. As the embryo matures, numerous scattered light-brown pigment cells develop over the large yolk mass and the body of the embryo. The eggs are removed from the petri dish with a pipette and placed into the rearing tank, Development within the egg progresses rapidly and hatching occurs about 24 hours after spawning. At hatching, the larvae retain a very large yolk sack and the eyes are not yet pigmented; the young drift belly up. Two days after hatching, the larvae have prominent pigmented eyes, are swimming with control, and begin feeding.
Tank raised juvenile Spadefish one year old, with three month old individual in the background. (Photo by: Stephen D. Walker) |
Feeding of the larvae is the critical point in the rearing of most marine Fishes. The larvae will only feed on living food items, but even newly hatched Artemia nauplii are too large for Spadefish larvae. It is necessary, therefore, to maintain a culture of live plankton to offer the young fish. Spadefish larvae are large enough to accept the marine rotifer Brachionus plicatilis as a first food. We culture rotifers and their food, the unicellular algae Chlorella sp., on a continuous basis in order to have them available when needed.
Spadefish larvae grow rapidly. Nine days after hatching they are able to take newly hatched Artemia. Unlike other marine species we have reared, Spadefish do not show a well defined point of metamorphosis. Most marine fish larvae are nearly colorless but pigmentation is present even in very young Spadefish larvae, though it is confined to the front half of the body. About day 15 pigmentation extends over the whole body and the young discontinue a planktonic lifestyle and begin to associate with the substrate. We consider this point to be metamorphosis. At 20 days, we move the juveniles out of the larvae tank and into a conventional aquarium with undergravel filtration. The young are then offered a wider variety of foods including flakes, ground shrimp, ground smelt, our standard gelatin diet, and baby and adult Artemia. Rapid growth of the juveniles continues and by four months they attain a length of 6 cm total length.
The larvae culture tank consists of a bare all-glass 20 gallon high (75- liter) aquarium. A gentle aeration is provided, but no filtration is used in order not to damage the delicate larvae. The tank is lighted by a fixture containing two 40 watt Vita-lite fluorescent bulbs and is timer-controlled for 18 hours of light daily. Twenty-five percent of the water in the rearing tank is removed each day and exchanged with the water from a conventional tank. This keeps ammonia and nitrite within acceptable levels. The tank is draped on three sides with a black plastic sheet to allow the larvae to see food more easily against the contrasting background.
Using the methods described here, we have been able to rear the young of eight separate spawnings to the juvenile stage. The numbers in each "batch" range from two to 50 individuals. The first young were reared from two eggs collected on September 21, 1989, and are both still doing well.
In researching sources for information on Spadefish reproduction it became apparent to us that very little was known on this subject. The only report of spawning behavior of any species in the family involves the observations of an aggregation of Spadefish presumed to be spawning in the wild (Chapman, 1978 (4)). Thresher (1984) indicates that no species in the family Ephippidae has been spawned and reared in captivity.
It is unfortunately true that spawning and rearing of marine fish by zoos and public aquariums is still not commonplace. We at the Tulsa Zoo are committed to broadening the knowledge in this area as far as our resources will allow. We are encouraged by our experiences and plan to continue working with Spadefish and other marine species.
Editor's Note: Although Spadefish are not commonly kept by marine aquarist, other members of the family are quite popular, such as the Long-finned batfish, (Platax pinnatus) or the Round-faced batfish (Platax tiera). When collected from the wild, theses batfish often have a difficulty adjusting to captivity. We hope this research will be a first step toward commercial production of these related aquarium species.
References: (web note: references were originally presented in alphabetical order)
1. 2. 3. 4.