C. R. Weirich, T. R. Tiersch
Abstract:
Only limited research has been conducted to investigate the effect of
salinity on the hatchability of channel catfish eggs, and no studies
have evaluated the effect of salinity on sac-fry development. This
study was undertaken to determine the percent hatch and development
of sac-fry from egg masses incubated at selected levels of salinity.
Sodium sulfite (0.75% NaSO3) was used to chemically dissociate
portions of egg masses and its effect on percent hatch was also
determined.
Experiments were conducted in four recirculating systems (one per
salinity treatment: 0, 1, 2, and 4 g/L NaCl). Each system was
equipped with a 3-ft^3 upwelling bead filter and 24 polyethylene
tanks (38-L), each supplied with blown air. Systems were filled 6 wk
prior to initiation of the study and NaC1 and CaC1 were added to
achieve desired levels of salinity and calcium (maintained at 50
mg/L). At the beginning of the study seven egg masses (2-3 d old),
obtained from a commercial producer, were each divided into 2
portions; one to be dissociated with NaSO3, the other to remain
undissociated. These portions were further divided into 4 groups, each
assigned to one salinity level. Undissociated egg masses were
weighed to the nearest 0.l g and placed into tanks. Dissociated eggs
were rinsed three times in flesh water, quickly transferred to form a
monolayer for image capture using a CCD video camera, and placed
into tanks. After hatching, sac-fry were siphoned from each tank to
allow image capture (for later determination of percent hatch) and
returned to tanks. In addition, a total of 25 sac-fry were removed from
each tank on the day of hatching and at 5 d posthatch to determine
wet and dry weights (to the nearest 0.1 rag). Ranges for water quality
parameters were: temperature, 27-29 C; pH, 8.1-8.7; and dissolved
oxygen, 7.7-8.6 mg/L. Total ammonia and nitrite-nitrogen levels were
below 0.8 and 0.1 rag/L, respectively. These parameters did not differ
among treatments throughout experiments. Data were analyzed by
ANOVA, and Fisher's LSD was used for means comparisons.
Percent hatch was significantly affected by salinity levels and NaSO3
treatment. Specifically, hatchability was increased for undissociated
eggs incubated at 1 g/L NaCl. No beneficial effect due to salinity was
noted for eggs incubated in 2 or 4 g/L and the latter treatment reduced
hatchability with respect to 0 g/L NaCI. Treatment of egg masses
with NaSO3 significantly reduced percent hatch at all NaC1 levels.
Wet and dry weights obtained for sac-fry hatched from undissociated
egg masses showed that wet weight gain and dry weight loss were
increased at a salinity 1 g/L.
(Louisiana Agricultural Experiment Station, Louisiana State
University Agricultural Center, Baton Rouge, LA 70803 USA)