Development of Fed and Starved Striped Bass (Morone saxatilis) Larvae from the Roanoke River, North Carolina

Abstract

Fed and unfed striped bass larvae were reared in a laboratory using ambient Roanoke River water to determine differences in growth and development. These differences were used to histologically determine the nutritional state of Roanoke River striped bass larvae collected from the Roanoke River delta and western Albemarle Sound from 1984 through 1986. An additional experiment examined the effects of high concentrations of aluminum in acidified waters on larval striped bass skin. Larvae that were given Artemia as a food source were successful at feeding by 6.5 days post—hatch. Decline in nutritional state of unfed larvae was apparent as soon as 5.5 days post—hatch. The organs and tissues showing signs of poor nutritional state were the eyes, liver, digestive tract, kidney, and trunk musculature. The pancreas may also be an indicator organ but results were not conclusive. Changes in these tissues occurred within 11.5 days post—hatch. Unfed larvae showed abnormal eye development by 7.5 days post—hatch. The livers of fed larvae showed moderate multifocal glycogen accumulation, while unfed larvae showed reduction in liver glycogen by 6.5 days post—hatch. Fed and unfed larvae possessed yolk 4.5 days after hatching; the rate of yolk absorption was highly variable In both groups. Fed larvae had distended, thick—walled digestive tracts; the guts of unfed larvae were collapsed and empty as soon as 4.5 days post—hatch. The hemopoietic tissue in the pronephric kidneys was reduced in unfed larvae 5.5 days post—hatch and older. Fed larvae had thickened, well—developed muscle fibers, while muscles of unfed larvae appeared thinner and separated as soon as 6 days post—hatch. Wild Roanoke River larvae examined histologically showed normal tissue development, Indicating that they were not in a starving condition. It is quite likely, however, that larvae dying from or weakened by starvation are easily preyed upon or are not susceptible to net capture. Results of the pH—aluminum experiment indicated that the microridge structure of the larval epidermis was severely altered In the presence of low pH (5.5) and high aluminum (680 ug Al3/l). Our results suggest that Roanoke striped bass larvae may suffer high mortality one to two days post—hatch from skin stress1 followed by a second mortality from starvation.