**3.1 Influence of temperature on hatch rate**

The influence of incubation temperature on hatch rate was investigated to establish the optimal temperature for incubating snook eggs. Embryos exposed to 23ºC water had the lowest mean hatch rate of 5.9% (range 0.8 to 11.4%) (Figure 3). The highest hatch rates of 23.5% occurred at 28ºC (range 21.7% to 27%). No significant difference in hatching rate (p> 0.05) was found between the 28ºC and 30°C treatment, but a significant difference (p<0.05) was found when 28ºC was compared to 26ºC and 23°C.

#### **3.2 Effect of egg stocking density on larval survival**

The effect of egg stocking density on larval survival at 14 DAH is presented in (Figure 4). At a stocking density of 375 eggs/l (High density) per tank, the mean survival from three tanks was 0.6%. Tanks stocked with a medium density (200 eggs/l) had a similar mean survival percentage with 0.5%. The highest survival was obtained at the low density stocking (100 eggs/l) with a mean overall 1.2% survival by 14 DAH (Figure 4). No significant difference (p> 0.05) was obtained between the high and medium density treatments, but a significant difference (p< 0.05) was obtained between the low density treatment and the other two.

#### **3.3 Influence of flow rate on larval survival**

Snook larvae were exposed to three different flow rates. Those fish exposed to no flow during the first 10 days (Figure 5) had a mean survival rate of 45% by 3 DAH, survival then

Fig. 3. Influence of temperature on percent hatch in snook larvae.

Fig. 4. Larval survival at three stocking densities at 14 DAH.

Fig. 3. Influence of temperature on percent hatch in snook larvae.

Fig. 4. Larval survival at three stocking densities at 14 DAH.

**High Density (375 eggs/L) Medium Density (200 eggs/L) Low Density (100 eggs/L) Stocking densities (eggs/L)**

**0.00**

**0.20**

**0.40**

**0.60**

**0.80**

**Survival rate (%)**

**1.00**

**1.20**

**1.40**

**1.60**

decreased to 19%by day 6. At 10 DAH, larval mean survival was only 5% from the initial stocking density. The slow flow (10 ml/min) treatment had a mean survival of 40% at 3 DAH, decreasing 3 days later to a 32% survival. Finally a mean survival of 21% was observed by 10 DAH (Figure 5). The third experiment had the lowest values in terms of survival. At high flow (30 ml/min), survival at 3 DAH was 16%, decreasing on Day 6 to a mean of 10% survival and by day 10 after hatch larval mean survival was 9% (Figure 5). No significant difference (p>0.05) was observed between the no flow and slow flow treatment at 3 DAH, but a significant difference (p< 0.05) in survival was found between all the treatments 6 and 10 DAH.

Fig. 5. Snook larval survival under three types of flow conditions.

#### **3.4 Effect of background phytoplankton in the water (Green water technique) on larval survival and growth**

Larvae were stocked in water with no algae and in water with algae (*N. occulata*) at a concentration of 1000/ml. Larvae tanks without algae are referred to as 'clear water' (Figure 6). The survival of larvae was significantly (p<0.05) influenced by the presence of *N. occulata* in the rearing water. The mean survival at 14 days post hatching in clear water was significantly lower at 0.17%, compared with 0.55% survival in green water tanks (Figure 6).

Length and myomere height in larvae from the clear water tanks had an average standard length (SL) of 3.20 mm and average myomere height of 0.70 mm (Figure 7); on the other hand, larvae in tanks subjected to green water technique had an average length of 3.34 mm and average myomere height of 0.73 mm. Although standard length and myomere height in the green water tanks were higher, no significant difference was found (p= 0.053).

Fig. 6. 14 DAH snook larval survival from tanks with *N. oculata* (Green water) and without phytoplankton (clear water)

**Type of Water used**

Fig. 7. Average snook larval length (SL) and myomere height from green water and clear water tank
