Thomas C. Ardelt, MS, DVM1; Michael R. Johnson, DVM,
During the last five years, reported cases of anemia in farm-raised
channel catfish from the Mississippi Delta have risen dramatically. Farmers refer to this
condition as "no blood" or "white-lip" disease. The anemia appears to
affect larger 1.5 - 2.0 lb. catfish, and the etiology is unknown. Severe anemia occurs
bimodally in October-November and in April-May. Last year, severe anemia (packed cell volume
C 10%) was documented in approximately 5% of cases at the Delta Branch Experimental Station,
but it is thought to be more prevalent due to unreported cases. In addition, the anemia may
run concurrent with other disease conditions (winter kill), thereby masking the
In an effort to document seasonal fluctuations in critical blood values
of channel catfish, a survey was conducted from September 1992 through January 1994. Packed
cell volume (PCV), total protein (TP), and osmolarity were recorded in 1633 fish from 6
different production ponds. Approximately 20 fish were sampled from each pond at each
sampling date. In addition, water temperature and fish weight were recorded.
Total protein and osmolarity remained fairly constant throughout the
year. However, catfish displayed a sinusoidal seasonal fluctuation in PCV. PCV was highest
in mid-summer (June, July, August) and lowest in mid-winter (December, January, February).
Mean values ranged from > 34% in midsummer to approximately 20% in mid-winter.
However, beginning in November, many fish displayed PCV values < 15% and several dropped
to < 10%. Fish were still alive and displayed no noticeable external lesions with the
exception of extremely pale gills. It is unknown why, in the same pond, some fish became
severely anemic while others did not.
In a concurrent study, a complete blood cell count (CBC) was run on 640
fish from October 1993 through January 1994 (the time of year when PCVs were lowest).
Sixteen channel catfish from four Delta production ponds were sampled bimonthly. The
following indices were recorded for each fish: PCV, TP, total red blood cell count (RBC),
hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration
(MCHC), mean corpuscular hemoglobin (MCH), total white blood cell count (WBC), percent and
absolute differential WBC count. Mean PCV was 22.7% with RBC 1.99 xl06cells/uL in October
while in December mean PCV dropped to 14.4% with RBC 1.49 xl06cells/uL. Mean MCV
went from 112 fL in October to 97 fL in December. The anemia was classified as microcytic,
normochromic and regenerative. Numerous polychromatic red blood cells (which in fish, are
smaller than mature RBCs) could be seen in all anemic fish, especially the most severely
There are three general pathophysiological mechanisms of anemia, 1.
reduced or defective erythropoiesis, 2. accelerated erythrocyte destruction, and 3.
hemorrhagic blood loss. Possibilities for reduced erythropoiesis include temperature or
seasonal effects (hormonal) on hematopoietic tissue, nutritional deficiencies (folic acid,
vit B12, iron etc.), or anemia of chronic disease. Accelerated erythrocyte destruction may
be caused by infectious agents, blood parasites, chemical toxins in the water, or
immune-mediated disorders. Hemorrhagic blood loss may be due to heavy parasite loads,
gastrointestinal ulcers, or hemostasis defects including disseminated intravascular
coagulation or other clotting disorders (Duncan and Prasse, 1986).
Seasonal fluctuations in PCV have been documented in other species,
e.g., trout and flounder (Demon and Yousef, 1975; Audet, and Claireaux, 1992; Mahoney and
McNulty, 1992). However, the fluctuations in these species are not as severe as those
recorded from channel catfish in our study. Denton and Yousef showed that seasonal changes
in rainbow trout hematology were not related to temperature or diet. They suggest that other
seasonal effects on activity and metabolic adaptations probably play an important role in
altering blood values. Our studies suggest that there may be a possible correlation between
temperature fluctuations and PCV fluctuations, and we are currently designing experiments to
further explore this relationship.
In conclusion, our study indicates that channel catfish in production
ponds undergo a sinusoidal seasonal fluctuation in PCV. During the time of year when PCV is
lowest, individual fish will display moderate to severe anemia. The anemia is characterized
as microcytic, normochromic and regenerative. Since it is regenerative we know that
hematopoiesis is taking place. Whether erythropoiesis is optimal during this time is
unknown. We have no evidence to support other pathophysiological mechanisms of anemia at
this time, but we certainly can not rule them out.
1. Audet, C. and Claireaux, G. 1992. Diel and seasonal changes
in resting levels of various blood parameters in brook trout (Salvelinus fontinalis).
Can J Fish Aquat Sci, 40:870-877.
2. Duncan, R.J. and Prasse, K.W. 1986. Veterinary
Laboratory Medicine, Clinical Pathology. 2nd ed. Iowa State University Press, pp.
3. Denton, J.E. and Yousef, M.K 1975. Seasonal changes in
hematology of rainbow trout, Salmo Gairdneri. Comp Biochem Physiol, 51A:151-153.
4. Mahoney, J.B. and McNulty, J.K. 1992. Disease-associated
blood changes and normal seasonal hematological variation in winter flounder in the
Hudson-Raitan estuary. Trans Amer Fish Soc, 121:261-268.