Water quality improvement by rockworm Marphysa sanguinea and its growth performance in the integrated culture with olive flounder

Abstract

Water quality improvement by rockworm Marphysa sanguinea and its growth performance in the integrated culture with olive flounder Hossein Parandavar Department of Fisheries Biology, The Graduate School, Pukyong National University Abstract Three trials have been conducted to test the water quality improvement and growth performance in the rockworm settlement tanks receiving wastes from olive flounder rearing tanks, in the integrated culture systems with flow-through and semi-recirculation. In comparison between culture systems, the pure production of the worm was 1.5 times higher in the flow-through system than in semi-recirculating system. Different effects on the removal efficiency appeared in different culture systems and among different treatments. In flow-through system, the highest removal efficiency showed in TN (56%) in G2 (0.6~1.5 g/initial weight), in TP (59%) in G1 (<0.5 g), in TSS (86%) in G2, and in COD (30%) in G3 (1.6~2.5 g). In semi-recirculating system, the highest removal efficiency was in TN (63%) in G2, in TP (53%) in G3, in TSS (80%) in G3, and in COD (21%) in G2. These results suggested that the rockworm M. sanguinea was an excellent potential candidate for integrated aquaculture and nutrient recycling including the removal of organic wastes in land-based systems. Experiment 1. Effects of rearing density on the growth of the rockworm Marphysa sanguinea Effects of density on the growth and survival of the rockworm polychaete M. sanguinea has been investigated in order to develop rearing techniques for this species. This study was conducted over a nine-month period in the Fisheries Science and Technology Center of Pukyong National University. Three rockworm densities, that is, 500, 1000 and 2000 worms/m2, were arranged to 3 groups (less than 0.5 g, 0.6~1.5 g, and 1.6~2.5 g) which were stocked in 0.10 m2 boxes with sand bottoms. The water flows continuously in the boxes and water temperature was maintained at 20 ± 2°C. All treatments were triplicated. Amount of food was 3.5% of body wet weight (3 times per week). Growth rate was checked with 15 randomly sampled rockworms from each box at months 3, 6 and 9. Results showed that SGRs were higher during the first 3 months (0~3 months) than during the second (3~6 months) and the third 3 months (6~9 months) in all treatments while SGRs decreased on the increase of density. However, survival rate and individual worm growth in high density was not better than in low density, but the daily biomass production was higher in medium and high density as 6.3, 13, and 14.7 g/m2/day in group of less than 0.5 g with 1000 inds/m2, in group of 0.6~1.5 g with 2000 inds/m2, and in group of 1.6~2.5 g with 2000 inds/m2, respectively. Result showed that M. sanguinea could be one of the most suitable species to commercially exploit in a farming system. In particular, specified densities permit elevated pure production. We suggest that further studies have to be focused on the effect of amount and kind of feed on growth of this species and estimated production costs. Experiment 2. Water quality improvement by rockworm Marphysa sanguinea and its growth performance in the integrated culture with olive flounder in the flow-through system Three expriments were conducted to test the effect of the rockworm M. sanguinea (Montagu) fed on commercial feed, fish feces and uneaten feed of olive flounder under controlled temperature conditions in integrated the flow-through system for 13 weeks. The fish grew in 3 groups between 0.69 to 0.75 g/day, and there was no significant difference in final weight (FW), weight gain (WG), specific growth rate (SGR), and survival rate (SR) in each experiment. The experiments on worms were done with 3 treatments using fish waste, with a treatment in starvation (control, without feed), and with a treatment using commercial feed. In group 1, worms with an initial weight (IW) of 0.34 g were fed. The pure production of harvested worms in T3 (4000 inds/m2; 891.8 g/m2) was significantly higher than in T1 (1000 inds/m2) and in T2 (2000 inds/m2) with 339.1 and 319 g/m2, respectively, in which fish feces and uneaten feed were fed (p<0.05). However, no significant difference was observed in pure production between in T1 and in T2. The highest removal efficiency of wastewater (TN, TSS, TOC, NH3, COD, NO2-N and NO3-N) in this group belonged to T3 with 51.6, 83.6, 23.7, 53.6, 19.6, 33.7 and 19.5%, respectively. In group 2, however, final individual mean weight belonged to T1 (500 inds/m2) and was significantly higher than in T2 and T3, but according to survival rate, the highest pure production belonged to T3 with 305 g/m2 in comparison to T1 (239 g/m2) and T2 (204.5 g/m2). Also, the highest removal efficiency of wastewater (TN, TSS, TOC, NH3, NO2-N and NO3-N) in this group belonged to T3 which were 56.4, 86.3, 31.3, 66.8, 27.6 and 31.6%, respectively. In group 3, worms with an IW (2.14 g) were fed the same as in the previous two groups. However, T3 (1000 inds/m2) had the lowest FW, WG and SGR in all other treatments, but it had the highest pure production (818 g/m2). The highest removal efficiency of wastewater (TN, TSS, TOC, NH3, COD, NO2-N and NO3-N) in this group belonged to T3 with 53.4, 83.3, 35.6, 55.6, 29.5, 36.4 and 29.4%, respectively. This study demonstrated that juvenile M. sanguinea in the flow-through system could grow readily by feeding on fish feces and uneaten feed of flounders as a food source, which was highly efficient, even though they did not grow and survive as well as those fed on commercial feed. Also, they were effective in the removal of wastewater. Therefore, this species is expected to be one of the candidates for integrated culture and wastewater recycling in flow-through system.

Experiment 3. Water quality improvement by rockworm Marphysa sanguinea and its growth performance in the integrated culture with olive flounder in the semi-recirculating system Three expriments were conducted to test the effect of rockworm M. sanguinea (Montagu) fed on commercial feed, fish feces and uneaten feed of olive flounder under controlled temperature conditions in integrated the semi-recirculating system for 14 weeks. The fish grew in 3 groups from 0.40 to 0.59 g/day and there were no significantly differences in FW, WG, SGR, and SR in each experiment. The experiments on worms were done with 3 treatments using fish waste, with a treatment in starvation (control, without feed), and with a treatment using commercial feed. In group 1, worms with an initial weight of 0.23 g were fed. The harvested biomass of M. sanguinea in T2 (2000 inds/m2) with 648 g/m2 was higher than that in T1 (1000 inds/m2) and T3 (4000 inds/m2) with 401.6 and 245.6 g/m2, respectively, which fed on fish feces and uneaten feed. However, in this group, highest pure production among treatments belonged to T5 (2000 inds/m2) with 1000 g/m2 which fed on commercial feed. The optimal removal efficiency of wastewater (TN, TSS, TOC and NO2-N) in this group belonged to T2 with 48.1, 78.4, 23.1 and 34.6%, respectively. In a similar setup for group 2, worms with an initial weight (IW) of 0.83g were fed. The final weight and pure production in T2 (1000 inds/m2) with 862 g/m2 was significantly higher than in T1 (500 inds/m2) and T3 (2000 inds/m2) with 481.2 and 142 g/m2, respectively. However, WG and SGR in T1 were higher than in T2 and T3. Also, in this group, the highest removal efficiency of wastewater (TN, TSS, TOC and NH3), which were 63.2, 75.9, 36.6 and 36.5%, respectively, belonged to T2. In group 3, worms with an IW (1.84 g) were fed the same as in the previous two experiments, but they did not grow very well and it seemed that they were not economic. However, the highest removal efficiency of wastewater (TSS, TOC, NH3, COD, and NO2-N) in this group belonged to T2 which were 80.2, 31.4, 42.3, 16.3 and 25.6%, respectively. As a result, weight gain decreased with the increase in worm density among treatments in 3 groups. SR, WG and SGR were the highest at the lowest density, whereas the final biomass and pure production were not influenced by density. This study demonstrated that M. sanguinea could grow readily by feeding on fish feces and uneaten feed of flounders as a food source, which was highly efficient, although they did not grow and survive as well as those fed on commercial feed. Also, they were effective in removal of wastewater, but they were not better than worms in flow-through system. Therefore, this species is expected to be one of the candidates for integrated culture and wastewater recycling in semi-recirculating system.

Keywords: Water quality improvement, Growth performance, Integrated culture, Rockworm Marphysa sanguinea, Olive flounder Paralichythys olivaceus.