CATASTROPHIC FISH MORTALITIES ON LAKE

Tennessee Stream Pollution Control Board Department of Public Health 620 Cordell Hull Building Nashville, Tennessee 37219

April 30, 1965, revised November 16, 1965 CATASTROPHIC FISH MORTALITIES ON

The first major die-off of fish on Kentucky Lake began early in January 1965 with thousands of rough fish (mainly Drum) dying below Pickwick Dam. By the time the epizootic had run its course (nearly five months) over two million figh weighing seven and one-half million pounds had died. The epi- zootic originating with Drum moved downstream involving in succession Buf- falo and Gizzard Shad. All available evidence pointed toward a microbial agent or agents rather than parasites or external stresses.

FISH KILLS AND EPIZOOTICS

The mortalities occurred when interest is rising in fish-pollution re- lations. Since 1961 the USPHS has been reporting, annually and by states, fish kills. Fish populations were also added as a parameter in the Public Health Service Water Pollution Surveillance System network. It is readily recognized that fish populations are unique in that they are their own in- dicators of water quality and are a parameter not affecting water use. The term "fish-kill" is ambiguous here, since the die off was a natural mortality due to an epizootic and not pollution related. Increasing em- phasis upon pollution and fish populations should not allow us to confuse "fish-kills" (due to industrial and municipal pollution) with epizootics.

Considering the number of parasites, bacteria, and viruses that fish are constantly subjected to, plus the environmental stresses they must adjust to, (though fish are mobile they are still considerably restricted) fish mortalities should occur periodically. Fisheries biologists have not yet learned all the complexities of fish populations in large like Kentucky Lake. The life histories of many fishes are unknown and more background data needs to be accumulated before fishery biologists can manage these reservoirs in full potential.

Fish kills in the last decade in Tennessee have decreased as new sewage treatment plants have reduced organic loads in streams. Prior to this, fish kills were to be expected in streams at dissolved oxygen sag points below certain cities during the summer. Industrial spills still occasionally decimate fish populations (e.g. Duck River, Elemental phosporus 1960), and some recent die-offs have been complicated by the presence of industrial wastes. Boone Reservoir in has a history of annual winter die offs, where high concentrations of zinc, ammonia, and copper have been detected. Several large mortalities of the gizzard shad on this reservoir were associated with Trichodiniasis, Myxosporidiasis, and Icthyophiriasis (all parasitic epizootics). Bacterial epizootics have been responsible for massive mortalities in Center Hill Reservoir and Old Hickory Reservoir (Both U. S. Corps of Engineer Reservoirs in ). Columnaris, a bac- terial disease, was implicated in both USCE Reservoirs.

Catastrophic Mortalities on Kentucky Lake

Kentucky Lake (the impounded section of the lower ) has nearly 160,000 surface acres at full pool and is one of the largest man made -2- lakes in the world. It was constructed by TVA primarily for flood control, navigation, and power production. The latter years in the twenty year his- tory of this lake have been marked by an inability of fisheries biologists to manage the lake satisfactorily for game fish production. This has been partially due to the lag between fisheries management recommendations and public acceptance of less restriction on commercial fishing gear and tech- niques. As a result of this epizootic, the case for adequate harvesting of rough fish has been considerably strengthened.

Recent surveys of the benthos (bottom organisms), by Tennessee Stream Pollution Control biologists, have demonstrated that this reservoir is re- latively unpolluted. The benthos belongs to the "clean water"gxoup of or- ganisms, and has been numerically rated at a biological index of 10 (the index being from 0 - 10, a lower number being a reflection of pollution). Fish populations have been exceptional, supporting an extensive sport and commercial fishery since impoundment. Mussel populations since impoundment have declined, not due to pollution, but rather to overharvesting and sil- tation (1965. Tennessee River Mussel Investigation. Tenn. Valley Authority). Fish kills and epizootics on this reservoir have prior to this been minor and infrequent.

Field Investigations of Mortalities

The first major die off was reported on January 20, 1965,and was taking place in the Savannah to Perryville section. According to figures (all mor- tality estimates from Game and Fish files) released by the Tennessee Game and Fish Commission, 99 per cent of the affected fish were Drum, the re- maining one per cent was mainly Buffalo with some Bluegills and Threadfin Shad. The kill affected an estimated 5,000 fish weighing 25,000 pounds. The second reported kill was investigated on February 1, 1965, and took place in the same section involving an estimated 68,000 fish weighing 315,000 pounds. Again the primary target was Drum, with some Buffalo and Carpsuckers also af- fected. The third kill reported on April 12, 1965, affected mainly Buffalo. By the middle of May the epizootic had subsided.

Table 1 Final Estimated Mortality Figures by Species

*Buffalo 2,000,000 Flathead Catfish 3,200 *Gizzard Shad 240,000 Yellow Bass 2,800 *Drum 180,000 Bluegill 2,800 Carp 11,000 White Bass 1,800 White Crappie 11,000 Black Bass (all 3 species) 1,100 Gar 4,200 Channel Catfish 1,100

*These three principal target species, by weight and number both, made up at least 80% of all total figures.

Symptoms

Autopsy of dying fish revealed the same symptoms for all species. Gross symptoms included exopthalmus, blood and water deposits under the scales, hemorrhaging gills, hypertrophied liver and kidneys, distended gall bladders, - 3 -

gastrointestinal tract empty, and abdominal cavity with an opaque or bloody fluid. These are all associated with hemorrhagic septicemia or dropsy which may be caused by several bacteria pathogenic to fish. Since the epizootic was presumed to be bacterial the symptoms of the fish can be termed as a severe case of bacteremia.

Parasitism

Many specimens of moribund fish were collected by the Tennessee Game and Fish Commission and shipped to the Fisheries Disease Laboratory at Auburn University. These had light to heavy gill infestations of parasitic protozoans including Trichodina, Scyphidia, and Chilodon. They concluded that these were not responsible for the mortalities.

Bacterial Cultures

Dying fish examined by the Stream Pollution Control biologists did not reveal any gross parasitological infestations, and symptoms of the moribund fish pointed to a microbial infection rather than external parasites. Un- fortunately the bacterial cultures isolated were only from the kidneys of a moribund Bluegill and a Threadfin Shad. The kidneys of moribund fish were exposed aseptically by cutting from the dorsal fin into the kidney, without contamination from the abdominal cavity. A sterile loop was then probed into the kidney for transfer to Trypticase Soy Agar slants. The kidney was chosen since contamination by a variety of bacteria involve many of the other af- fected organs such as gills and skin etc. Resulting cultures were then trans- ferred to a number of media including Pseudomonas Agar P and F and Centrimide Agar. The isolated organism grew rapidly on all three of these selective media. The bacterium involved in the epizootic has been tentatively iden- tified as Pseudomonas fluorescens.

Causative Agent

Investigations of fish mortalities in Europe have shown that Pseudomonas may be an opportunistic secondary invader, following a primary lethal filtrable virus (1963. Nikolsky. The Ecology of Fishes.). This is entirely possible in the case of the Kentucky Lake mortalities. The role each agent plays has not been adequately defined. Tets (1965. cited in Sport Fishery Abstracts 10(1):50, translation of abstract) subjected carp to infection with the ulcerous form of contagious dropsy and from June to autumn the experimental fish were not sick. He concluded that the ulcerous form is not contagious in summer. The parallels between Tets' work and these winter epizootics is more than coincidental.

Estimates of Mortalities

Final estimated figures on this mortality were approximately two million fish weighing approximately seven and one half million pounds. The lower section of Kentucky Lake in Kentucky and the lower section of Pickwick Reser- voir in had reported kills in April and May, but these were light compared to the kill discussed above. (38,000 no./39,000 lbs. Alabama, and 380,000 no./182,000 lbs. Kentucky).

Epizootic FOCI (see map and Table 2)

The mortality has been broken into seven reservoir areas according to available figures. The first three outbreaks were in the upper pool of Ken- tucky Lake (from Pickwick Dam to New Johnsonville) and the principal target species was Drum.

The entire Kentucky Lake pool was involved in foci four from April 12 to May 16. The prime target species being Buffalo with over two million fish dying. FOCI five and seven (late April and early May) were in Alabama in the lower Pickwick Reservoir pool. Again Buffalo was the target species, with thirty-eight thousand being involved in all. FOCI SIX, in the Kentucky section of Kentucky Lake, was observed on May 1 and 2 and involved 220,000 Gizzard Shad along with 110,000 Drum and 29,000 Buffalo.

The general trend appears to be an outbreak originating around January 20th below Pickwick Dam involving mainly Drum. As the epizootic spread down- stream the prime target species was Buffalo, and finally in the last down- stream section, Gizzard Shad.

Table 2 Mortality Estimates With Species Comparison

Number % Number Weight (lbs) % Weight

Pickwick Lake (Ala.) - mi. 236 to 214.3 - April 27, 1965 (FOCI 5)

Buffalo 380 40.1 2,000 67.5 Drum 340 35.3 670 22.8 Gizzard Shad 160 17.3 41 1.4 *Totals 950 2,900

Pickwick Lake (Ala.) - mi. 241 to 214 - May 6, 1965 (FOCI 7)

Drum 32,000 86.5 27,000 73.0 Buffalo 2,400 6.6 6,000 16.4 *Totals 37,000 36,000

Kentucky Lake (Tenn.) - mi. 214.2 to 49.2 - April 12-May 16, 1965 (FOCI 4)

Buffalo 2,000,000 95.7 7,000,000 97.2 *Totals 2,100,000 7,200,000

Kentucky Lake (Ky.) - mi. 49 .2 to 22.4 - May 1 and 2, 1965 (FOCI 6)

Gizzard Shad 220,000 58.2 16,000 8.9 Drum 110,000 28.9 21,000 11.6 Buffalo 29,000 7.6 130,000 72.9

*TOTA LS 380,000 180,000 *Including other species -5-

Target Fish Species (see figure and Tables 1 and 2)

Only three species were prime targets during this epizootic, Buffalo- two million; Gizzard Shad - two hundred and forty thousand; and Drum - one hundred and eighty thousand. Nine other species or species-group numbered from eleven hundred to eleven thousand each and percentage wise were insig- nificant.

Buffalo with the exception of the Old Hickory epizootic, have never been involved in such mass mortalities. Drum have been more susceptible to epi- zootics in Tennessee. Both fish are bottom feeders, and with an increase in the availability of the introduced clam (Corbicula), high populations of these fish have developed. Limited harvesting of these rough fish has also contributed to excessive populations. Shad (including the Gizzard and Thread- fin) are known for massive winter kills, due to drops in temperature. They are also very susceptible to external parasites. On Boone Reservoir Gizzard Shad are liable to Trichodina infestating the gill filaments. During one such winter kill Trichodina were even packed within the head canals. The zoochlorellae within the massed Trichodina caused the head canal system to appear green.

The fish names used herein are those listed by the Tennessee Game and Fish Commission (1965. Glenn Gentry, Common and Scientific Names of the Fishes of Tennessee, Tenn. Game and Fish Comm.): Threadfin Shad, Dorosoma petenense; Gizzard Shad, Dorosoma cepedianum; Carp, Cyprinus carpio; Buffalo, Ictiobus ssp.; Carpsucker, Carpiodes ssp.; and Freshwater drum, Aplodinotus grunniens.

Discussion

There are parallels in this and the Hiwassee River (1955) and Old Hickory Reservoir (1962) epizootics. The mortality on the former involved mainly Drum. The latter involved Carp mainly, with Shad, Drum, and many large Buffalo. As in Kentucky Lake, the Catfish population was relatively unaffected. An un- identified Pseudomonad was readily isolated from the Carp on Old Hickory.

Both parasitic (Protozoan) infestations and microbial epizootics may affect a specific fish species while other species escape with limited mor- talities. This has also been noted in outbreaks of disease in tropical fish aquariums. Rock and Nelson (Prog. Fish Cult. 27:138) reported an Aeromonas (which is another Pseudomonad) epizootic which first involved Channel catfish and was followed in succession by Gizzard Shad mortalities. The Pseudomonad bacteria, Pseudomonas fluorescens and Aeromonas liquefacians, are widely distributed in surface waters. Fish become highly susceptible to them when stressed by crowding, external parasites, viruses, and physical environmental changes.

Conclusions

Epizootics like fish kills may be spectacular, however, they rarely have any lasting effects on fish populations. It is regrettable, even though the effects may be good in thinning rough fish populations, that fish resources are thereby wasted. Results from this massive epizootic on Kentucky Lake indicate the need for a more efficient system of reporting catastrophic mortalities whereby field investigations can be carried out during all stages of an epizootic. Techniques of sampling and estimating total species involved, number, and weights need improvement. Diagnostic procedures for bacteria and parasites appear adequate. Mass mortalities of fish, caused by disease and parasites, have been frequent on large streams and reservoirs in Tennessee, and while spectacular they are only an indica- tion of an unharvested renewable natural resource. Duration,river miles affected, number of fish killed, and target species affected all mark the Kentucky Lake epizootic as unique. Also this was the first major die off in the twenty year history of this reservoir.

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TARGET SPECIES

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Buffalo Gizzard Shad 2,000,000 240,000

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