3. Results
3.1. Effects of algal presentation in larÕal deÕelopment Seabream larvae had a growth of around 10 per day throughout the experimental
Ž .
period under all the treatments tested Fig. 1 . Paired comparisons between the slopes of
Ž .
Ž .
Fig. 1. Growth of seabream larvae in the presence of freeze-dried left column and live right column N. Ž
gaditana supplied with rotifers previously fed N. gaditana, I. galbana and commercial enricher Protein .
Selco .
the growth equations revealed no difference when live or freeze-dried N. gaditana were used in the larval tanks. Neither was there any significant difference in growth rate
Ž between treatments LF and FF, LI and FI, and LP and FP P 0.05; see Table 2 for
. abbreviations . Therefore, the use of freeze-dried N. gaditana in the mass rearing of
seabream larvae did not affect their growth rate with any of the three different types of rotifer enrichment used.
Slight but significant differences in growth were found between the enrichments. Larvae that received rotifers enriched with freeze-dried N. gaditana had a lower growth
Ž .
rate P - 0.05 than those fed rotifers enriched with freeze-dried I. galbana or the
commercial enricher. No differences in growth rate were found between the latter two Ž
. enrichments P 0.05 .
Survival after 43 days was not affected either by the use of freeze-dried N. gaditana Ž
. in the larval tanks or by the type of rotifer enrichment P 0.05 , achieving similar
Fig. 2. Survival and biomass obtained at the end of the experiment with seabream larvae using live and Ž
. freeze-dried N. gaditana in larval tanks and rotifers fed three different diets. Homogeneous groups P 0.05
are denoted by a and b.
Ž .
values of around 15 in all instances Fig. 2 . Larval density decreased gradually, without peaks of mortality or cannibalism throughout the trials.
Ž .
The use of freeze-dried N. gaditana in larval tanks had no effect P 0.05 on final Ž
y1
. biomass mg dry weight l
, as revealed by paired comparisons between treatments. On the other hand, the type of rotifer enrichment influenced the final biomass attained
Ž .
Fig. 2 . Use of rotifers enriched with freeze-dried I. galbana or Protein Selco produced Ž
.
y1
similar biomass P 0.05
of 19 1.4 and 16.5 2.1 mg l , respectively. The
biomass achieved using rotifers enriched with freeze-dried I. galbana was higher Ž
. Ž
. P - 0.05 than that obtained with use of rotifers enriched with N. gaditana Fig. 2 .
Ž .
Fig. 3. Ammonia and nitrite concentration in tanks with seabream larvae receiving freeze-dried left column Ž
. and live right column N. gaditana. The first segment in each graph corresponds to the regression obtained
for the period of stagnant water, and the second segment corresponds to the water exchange period.
3.2. Effects of freeze-dried algae on water quality during larÕal deÕelopment Of the four parameters studied, ammonia was the one that varied most according to
the use of freeze-dried or live N. gaditana in the larval tanks. Ammonia increased more during the period of stagnant water when freeze-dried algae was used, and was
significantly higher on day 16 for freeze-dried N. gaditana compared to the use of live Ž
. algae P - 0.05, Fig. 3 . However, the increased water exchange from day 16 led to
Ž .
similar ammonia concentrations at the end of the experiment day 43 , being 0.62 0.07
y1
Ž .
and 0.53 0.08 mg l , respectively P 0.05 . The fraction of unionized ammonia
Ž .
Ž .
NH was also higher for freeze-dried algae
P - 0.05 . From day 13 to day 18 of
3
Ž .
Fig. 4. pH and dissolved oxygen in tanks with seabream larvae that received freeze-dried left column and Ž
. live right column N. gaditana.
culture, a mean value of 0.051 0.015 mg l
y1
NH was recorded, in comparison to
3
0.027 0.014 mg l
y1
NH achieved for the same period when live N. gaditana was
3
Ž .
present in larval tanks. The variation in pH was similar P 0.05 between treatments and decreased gradually from around 8.15 at the beginning to 7.85 at the end of the
Ž .
Ž .
trials Fig. 4 . Oxygen concentration did not change P 0.05 depending on algal
Ž .
presentation and had a slow constant decrease throughout the rearing process Fig. 4 . Nitrite concentration was lower than 0.1 mg l
y1
NO
y
and did not vary during the
2
first 15 days between tanks that received freeze-dried N. gaditana and those fed live N. Ž
. gaditana P 0.05, Fig. 3 . From the beginning of water exchange onwards, an increase
in nitrite concentration occurred when both types of algae were used. This increase was Ž
more pronounced when live N. gaditana was added to the larval tanks P - 0.05, Fig. .
3 .
4. Discussion
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