World Aquaculture March 2019

34 MARCH 2019 • WORLD AQUACULTURE • WWW.WA S.ORG from the harvested seaweed in each tank. Each sample was placed in a small plastic basket and given a quick 30-sec rinse with potable fresh water to remove excess salt. The seaweed samples were cleaned by hand to remove any fouling ( Ulva spp., Chaetomorpha spp. and amphipods). Each sample of Gracilaria was placed in an aluminum foil tray, weighed and placed in a drying oven for 72 h at 50-65 C. The samples were weighed daily to ensure that constant dry weight (DW) was achieved. To determine seaweed growth, the weekly harvest (g WW) from each tank was converted to DW to calculate productivity (g DW/m 2 d). A one-way ANOVA indicated that there were significant (p < 0.05) growth differences. A post-hoc Tukey HSD test indicated that the growth rate at 100 percent sunlight (11 g DW/m 2 d) was significantly greater than the growth rate at 25 percent sunlight (4 g DW/m 2 d), but growth arate at 50 percent sunlight (7 g DW/ m 2 d) was not significantly different that at 100 percent or 25 percent sunlight (Fig. 6). In this study, Gracilaria growth at 100 percent sunlight was half of the expected value of 22-25 g DW/ m 2 d(Hanisak and Ryther 1984, Hanisak 1987). Growth may have been stunted from substantial summertime fouling of seaweed and tank walls. In addition, aeration of the rectangular tanks did not always maintain uniform distribution of the seaweed. Good aeration is beneficial to seaweed growth in tank culture for a multitude of reasons: increased photosynthetic efficiency, enhanced increased nutrient uptake rates, greater availability of carbon dioxide and oxygen, and reduction of epiphytes (Hanisak 1987). Nutritional Profile of Seaweed At weeks 0, 2, 4, 5 and 6, dried seaweed samples were ground with a mortar and pestle into a fine powder. Samples (10-25 g DW each) were shipped to New Jersey Feed Lab for analysis of moisture, protein, fat, ash and carbohydrates. Dry weight results of percentages of each constituent were re-calculated to obtain moisture-free values to assist with comparisons. A one-way ANOVA with a post-hoc Tukey HSD test was used to determine if there were statistical differences (p < 0.05) between weeks and between treatments. There were no difference between weeks for each treatment, however, there were differences between treatments (Fig. 7). The seaweed was highest in carbohydrate content (41- 43 percent) when compared to proteins, ash and fats. The carbohydrate content of seaweed at 50 percent sunlight was significantly less than that at 25 percent sunlight. The carbohydrate content of seaweed at 100 percent sunlight was not significantly different from that at 25 percent or 50 percent sunlight. The seaweed was also high in ash (29-33 percent) and the ash content at 100 percent and 50 percent sunlight were not significantly different, although both were greater than the ash content at 25 percent sunlight. The seaweed was high in protein (25-28 percent). The protein content of seaweed at 100 percent sunlight was significantly lower than that at 25 percent and 50 percent sunlight, which were not significantly different. The fat content of seaweed was nominal (0.11-0.17 percent) and there were no significant differences among sunlight intensity treatments. Overall the nutritional profile of seaweed was similar among TABLE 1. Water quality parameters measured during the study in the six seaweed tanks. All parameters were within acceptable ranges for seaweed culture. Dissolved Alkalinity Ammonia Nitrite Nitrate Oxygen (%) pH Salinity (ppt) Temperature (C) (mg/L as CaCO3) (mg N/L) (mg N/L) (mg N/L) Mean 107 8.40 29.8 29.5 154 0.00 0.100 3.7 Range 92–121 7.49–9.39 27.0–32.8 24.4–34.4 140–170 0.00–0.05 0.065–0.178 1.7–7.8 n 504 504 504 504 144 108 108 108 LEFT, FIGURE 6. Average growth of Gracilaria tikvahiae at three sunlight intensities. Standard deviation is represented by the error bars (n=7 samples; starting values and six weekly values). Statistical differences between treatments are represented by letters. RIGHT, FIGURE 7. Nutritional profile of Gracilaria tikvahiae cultured in the three sunlight treatments. Standard deviation is represented by the error bars (n=7 samples; starting values and six weekly values). Statistical differences between treatments for each nutritional component is represented by a, b, c letters.