Captive Care Notes: Herrings and Shads (Family Clupeidae)
Pelagic (open water), schooling fishes like herrings and shads are poor subjects for the home aquarium since they're accustomed to swimming across great distances in vast, unimpeded expanses of water. Life in the glassy confines of an aquarium is simply too confining. Herrings and shads are extremely nervous unless they are kept in large schools, and overly sensitive to vibrations and the sudden turning on-and-off of lights. Frightened herrings bash themselves against the aquarium glass as if trying to break through it, and they easily lose their loose-fitting scales, which, for such delicate fishes, is almost always fatal. For these reasons, herrings and shads are best left in the wild, or to large public or laboratory aquaria that can accommodate their spatial and schooling needs.
But if you're the type of aquarist who enjoys a challenge, then keeping herrings and shads will pose just that. First, forget about obtaining mature specimens from the wild. Their reputation for immediately dying if you so much as touch them with a net is legendary. And should one survive the net, it will almost certainly beat itself to death against the sides of a collecting bucket or transport container unless anesthetized. Instead, the key to maintaining Alosa species in aquaria is to get them while they're still larvae, or newly post-larval, and let them mature under captive conditions. It's not that Alosa juveniles are less delicate than adults -- they aren't. (They see a net and die, joked one biologist I spoke with.) Rather, the advantage of keeping juveniles is that their size allows them to be transported without netting or lifting them out of the water. Be mindful, though, that juvenile Alosa are sensitive to water turbulence. In fact, hatchery workers are so paranoid about this sensitivy that they take great care to avoid turbulence when pouring juveniles from one container to another. Instead, gently corral them into a wide-mouth container and then let them swim out on their own accord. Another, perhaps greater, advantage is that it is easier to maintain a large school of juvenile Alosa than a large school of adults. Schooling, even to the point of overcrowding, appears to be the secret to keeping captive alosines happy.
According to fisheries ecologist Karin E. Limburg, laboratory experiments on American Shad Alosa sapidissima metabolic rates in response to schooling density show that a good rule for keeping shad is definitely "the more, the merrier" (K. E. Limburg, pers. comm.). The more shad that were in a tank, the lower their metabolic rates. "I'm sure there's a break-point where oxygen stress and the buildup of ammonia would counteract the benefits of schooling with large numbers of other shad," Dr. Limburg adds, "but we certainly did not reach that threshold." Finally, Dr. Limburg advises that sea salt is a great aid in times of stress. She used a salt solution of 5 ppt when she transferred fish, and found that larvae had the lowest mortality and best growth at 10 ppt (as opposed to 0 and 20 ppt).
Feed juvenile Alosa live baby brine shrimp. As they grow they can sometimes be weaned over to fine grain foods, but small live foods, such as adult brine shrimp, should always be part of their diet. Aquaria should be as large as possible, with a large, open swimming area and efficient (but gentle) wet/dry filtration. Also consider a circular rank; shad larvae swim constantly and tend to accumulate in the corners of a rectangular tank. Other tankmates are not recommended. In the aquarium, alewives are said to be aggressive towards other fish; when food enters the water they swarm into the food and consume it while the other fish retreat to the side and don't feed.
Acquiring larval and juvenile Alosa may be as difficult as keeping them. Catching them in the wild seems impractical, since locating juveniles would require knowing when and where the parents spawned, and where the juveniles are feeding. A more reliable source would be hatcheries where Alewive Alosa pseudoharengus are raised for bait. Educators may wish to contact the Chesapeake Bay Foundation, which supplies larval shad and equipment to select Maryland and Virginia schools.
Few public aquaria exhibit Alosa, partly because of their difficulty, but mostly because they are not "sexy" fish that sell tickets. One facility that does is the National Aquarium in Baltimore (NAIB), which maintains a circular, 22,000-gallon "schooling" tank with approximately 800 Alewives. NAIB aquarists collect the Alewives from freshwater ponds in New Jersey, where they are raised commercially. During the night the fish are attracted to lights, which are strategically placed to draw them into small impoundments. In the morning the gates to the impoundents are closed and the fish are easily (but gingerly) collected. The Alewives (about 1000 per load) are shipped to NAIB in a special truck outfitted with a 10-foot round tank. Back at NAIB the Alewives are slowly conditioned to salt water (31 ppt) during a 30-90 day quarantine period. Once on display, the outflow of the tank's sand filter system forces the fish to swim in one direction. Eventually the fish develop ulcers on one side of their mouths, presumably from rubbing up against the acrylic walls of the tank. This is remedied by reversing the direction of the flow. Since the alewives are constantly swimming, they are fed a high-energy diet of small krill in the morning and Tetramin flakes throughout the day with the use of an automatic feeder. Once the Alewives are settled in the aquarium, scale loss is minimal. Their life expectancy on display is 1-2 years (R. Bromwell, pers. comm.).
Little has been published on the aquarium care of Gizzard and Threadfin Shads (Dorosoma). In one laboratory experiment, Threadfin Shad were maintained in 40-gallon tanks on a diet of live daphnia, chironomid larvae (bloodworms), and tubifex worms. The fish were quite proficient at digging out food that was buried in the sand. A key to their captive survival, it seems, is light handling and quick transport from the field. Native fish enthusiast Michael Hissom dip nets Threadfin Shad as they congregate at the bottom of a lake spillway. Here the fish are easy to catch -- which reduces handling-related stress and loss of their deciduous (easily shed) scales -- and are immediately taken home in an aerated bucket. (Adding some salt to the water also helps reduce stress.) Hissom keeps about a dozen Threadfin Shad in a 125-gallon aquarium where they feed on micro-pellets. McLane (1955) reports catching Threadfin Shad at night with a flashlight; the fish were attracted to the beam and literally jumped out of the water onto dry sand at McLane's feet. Gizzard Shad are displayed at the Mississippi Museum of Natural Science in Jackson, but even here aquarists admit that the fish are delicate and that few of the shad they catch -- about one in 200 -- survive the journey from stocking ponds to the aquarium. The few that do survive, however, readily accept prepared food and live a long time (R. Weitzell, pers. comm.).
As with most migratory fishes, Alosa will not naturally spawn in aquaria since the environmental cues that induce spawning (as far as they are known) are too complex to be simulated. But Alosa are artificially spawned at hatcheries in one of two methods. Most "low-tech" hatcheries are located directly on the rivers where the young are to be released. Hatchery workers collect ripe males and females as they return to spawn. They squeeze the female's eggs into a shallow bowl or bucket and fertilize them by gently stirring in sperm from the males. The eggs are then placed into hatching tanks that are continuously refreshed with water pumped from the river. As the newly hatched fry mature, they make their way through a pipeline that whisks them to their permanent home.
A more "hi-tech" hatchery approach allows shad to spawn on their own with the help of hormone injections. Migrating Alosa are collected from the wild, dipped into an anesthetic to keep them calm, sexed, and tested to see if their eggs and sperm are sufficiently developed for the hormone to work. A glass pipette is inserted through the vent and into the testes and ovaries and small samples of eggs and sperm are removed, which are then examined under the microscope. If a fish is ready, it's given a hormone injection -- a grain of rice-sized pellet with the consistency of an aspirin. Since mortality is high from the rough handling, hatchery workers also mix non-injected specimens in with the injected ones. Hormones released during the induced spawning process cause the non-injected fish to spawn as well. The resulting orgy-like spawning act, described below, is summarized from a 1997 hatchery report from the Maine Department of Marine Resources:
In June and July 1997, around 30 American Shad were injected and released into a 3,030-gallon, naturally lit spawning tank. During the day, the shad swam parallel to each other, usually against the current. But as the hormones took effect and the afternoon waned, the shad got more excited and unpredictable in their movements. First, occasional individuals "changed lanes." Then they began doing U-turns and 360-degree loops around the tank, now usually with the current. Then this looping turned into sudden high-speed bursts, with individuals racing around the tank one to 1-1/2 times. Now the shad also began to get more aggressive. A male approached a female from the rear and attempted to touch his nose to just in front of her tail. The female didnšt seem to like this, and so the two shad, as a pair, chased around for one or two circuits of the tank, often splashing and slapping on the surface (the behavior shad anglers call "washing"). However, the fish had not yet spawned. Instead, the high-speed, pair-swimming behavior apparently serves as a way to get the other shad more excited. As darkness fell, more and more shad seemingly lost their inhibitions and began falling out of their parallel swimming patterns. The number and frequency of aggressive encounters, along with the U-turns and 360-degree loops, continued to increase as the evening wore on. Eventually, the aggressive pairings became mutually agreeable and spawning occurred. Each pair of spawning shad swam in tight 360-degree loops, during which they vibrated or jerked spasmodically, with the inside shad pushing against the outside shad's body. During these encounters eggs and sperm were squeezed out. Apparently, the sight (or scent?) of these spawning shad incited unpaired shads to swim in vibrating circles by themselves. Since they do not have a mate to help them release eggs and sperm, they availed themselves of whatever was in the water, pushing, bumping, or vibrating against filter pipes and the tank walls. One individual shad was observed several nights in a row slowly bumping its side against the tank in what seemed like a choreographed manner. It would visit the same several spots on the tank wall, bump it gently several times, then swim to another spot and repeat the ritual. After several stops the shad would reverse direction, swim directly back to the original spot, and begin the pattern again. Hatchery workers who placed their fingers against the tank glass could detect some of these vibrations, which were described as "much like [that of] a low frequency vibrator pad." In this particular tank, the shad produced 0.2-2.3 liters of eggs nightly, at an average of 82,700 eggs per female.
Threadfin Shad are cultured in nursery ponds and stocked into reservoirs and lakes to provide forage for gamefish. (Fishery managers prefer Threadfin Shad over Gizzard Shad because their smaller size makes them easier for predators to swallow.) Nursery ponds are seeded with a fertilizer, such as fresh cow manure, in order to stimulate a bloom of plankton. Shallow portions of the ponds are stacked with six-inch bales of hay to provide a place to spawn. Since overfertilizing, overfeeding, or too much hay can deplete oxygen levels, especially during the summer, an emergency water supply is recommended. As long as nursery ponds are free of predators, a yield of 50,000-100,000 Threadfin Shad per acre is possible.