EFFECT OF VARIOUS DIETARY SEAWEEDS ON THE GROWTH OF GOLD-MOUTH TURBAN ( Turbo chrysostomus L . , 1758 ) AT LOMBOK , INDONESIA

Gold-mouth turban (Turbo chrysostomus L., 1758) is an important source of protein for coastal people in Lombok, West Nusa Tenggara, Indonesia. In order to acquire its seed production technique, research on the culture of the species was carried out since 2012. Feed source is a key concern when culturing animal, including turban snail. Growth of gold-mouth turban fed with seaweed Gracilaria sp., Ulva spp., and Kappaphycus alvarezii was evaluated. Each diet was randomly assigned to triplicate groups of 30 snail juveniles with an initial body weight and shell length of 4.65 ± 0.00g and 24.55 ± 0.08mm, respectively. After six weeks feeding trial, snails fed with Gracilaria sp. diet had significantly higher (P<0.05) in final weight, final shell length, weight gain, specific growth rate (SGR) and food intake compared to snails fed with Ulva spp. or K. alvarezii diets.


INTRODUCTION
Gold-mouth turban or Turbo chrysostomus is a marine gastropod belongs to family Turbinidae.Turbinid species have been identified as herbivorous marine invertebrates (Kikutani et al., 2002;Quiñones and Michel-Morfín, 2006), and consumes macroalgae around their habitat (Wernberg et al., 2008).This species was collected as a protein source by local people living in the coastal area of Lombok island, West Nusa Tenggara, Indonesia.To acquire its seed production technique, research on the culture of the species was carried out since 2012.Knowledge of suitable feed is an important aspect in the success of animal culture practice.Gut content analysis of Turbo brunneus showed that their diet comprises mainly of Rhodophytes such as Hypnea sp., Ceramium miniatum and Gracilaria sp.(Ramesh and Ravichandran, 2008).Juvenile of Turbo sarmaticus could consume and digest red algae (Gelidium pristoides and Corralian spp.), green algae (Ulva rigida and Codium extricatum) and brown algae (Ecklonia radiate and Inyengaria stellata) at the rate of 1.45% to 9.5% of body weight per day (Foster and Hodgson, 1998).
Preliminary observation showed that goldmouth turban consumed Gracilaria sp., and general preference of turban shells indicated that turbo could eat Rhodopyhta, Chlorophyta or Phaeophyta (Foster and Hodgson, 1998).Therefore, this study is intended to examine the effect of different dietary seaweeds or algae (Gracilaria sp., Ulva spp.and Kappaphycus alvarezii) on the growth of gold-mouth turban.

Experimental Diets
In this study, Gracilaria sp. and K. alvarezii were purchased from a local farm in Sekotong, West Lombok, and Ulva spp.were collected from Gerupuk waters in Central Lombok, Indonesia.Juvenile gold-mouth turban were fed with the algae every two days at a level of 40% of the total body weight within six weeks of feeding trial.

Feeding Trial
Two hundred and seventy hatchery-reared juvenile gold-mouth turban (Turbo chrysostomus) of six months old was used in this study.Those juveniles were produced in the hatchery of Mataram Marine Bio Industry Technical Implementation Unit, Indonesian Institute of Sciences (LIPI).The feeding trial was carried out for six weeks from 4 November to 18 December 2014.Juveniles were divided into three groups of 30 individuals for three replicates of each treatment.Juveniles have an average of initial body weight and shell length of 4.65±0.00gand 24.55±0.08mm.Juveniles were placed into nine experimental plastic tanks containing 10L of filtered seawater.A set of control for each diet was established, i.e., a reservoir containing diet without any juvenile, intended to monitor growth and decomposition rates of the diet (Table 1).Each tank was equipped with continuous aeration, placed in the outdoor laboratory with a natural light cycle, and covered with 3mm mesh size plastic netting to reduce the sunlight and prevent the juvenile creeping out from the tank.Two-inch PVC pipe that cut longitudinally were placed in the bottom of the tanks, provided a shelter for the snails.The tanks were cleaned every two days to remove uneaten diet and fecal material, and at the same time, 75% of the water were changed.Uneaten diets were weighed to calculate food intake.During the study, water temperature and salinity were recorded periodically.Every two weeks, all snails were weighed individually with a digital balance (0.01g scale) and shell length measured using an analog caliper.

Growth Performance
Growth performance was evaluated based on weight gain (WG), specific growth rate (SGR), food intake (FI), food conversion ratio (FCR) and survival rate (SR).Growth performance parameters were calculated according to Bautista-Teruel et al. (2003) with equations as follow; WG (%) = 100 x (W t -W 0 ) / W 0 SGR (% day -1 ) = 100 x [(ln W t -ln W 0 )/t] FI (g ind -1 ) = total food intake (g) / N FCR = total food intake (g) / total wet weight gain (g) SR (%) = 100 x Nt / N0 Where W o (g) is the initial mean body weight, W t (g) is the final mean body weight, t (day) is feeding period, N is number of snail in each tank, N 0 is number of snail at the start of trial and N t is number of snail at the end of trial.

Statistical Analysis
Data were analyzed by one-way analysis of variance (ANOVA) using SPSS 18 software

RESULTS
Water quality measurements during the study showed that the water temperature in the experimental tanks varied from 23 to 26 o C, while the salinity ranged from 30 to 40‰.
The growth data of gold-mouth turban (T.chrysostomus) fed with different seaweed diets were presented in Table 2. Final weight, final shell length, weight gain, specific growth rate (SGR) and food intake of snails fed with Gracilaria sp. were significantly higher (P<0.05)than the other diet treatments.Snails fed with Ulva spp.and K. alvarezii showed a decrease in weight gain and SGR.However, the growth of snails fed with Ulva spp.were slightly (40%) higher than snails fed with K. alvarezii.The maximun food intake was achieved in snails fed with Gracilaria sp., while food intake of Ulva spp., and K. alvarezii were 92% and 75% lower than food intake of Gracilaria sp., respectively.Survival rate (SR) of snails fed with K. alvarezii was significantly lower than those of snails that received the other two diets.

DISCUSSION
In the present study, Gracilaria sp.promotes positive effect on the growth of snail T. chrysostomus during six weeks of feeding trial with the average weight increase of 0.08g or 1.72% of initial weight.Previous study on abalone Haliotis asinina showed that Gracilaria heteroclada could increase the weight up to 2g in 45 days of feeding trial (Capinpin and Core, 1996).The same trend of weight gain has also been found in abalone H. tuberculata coccinea Reeve fed with G. cornea reared for sixty days resulting in increase of more than 0.2g (Viera et al., 2005).It seems that seaweed Gracilaria sp. as a feed source was more efficient in abalone than in gold-mouth turban.However, weight gain of gold-mouth turban fed with Gracilaria sp. was higher compared to weight gain of gold-mouth turban fed with Ulva spp.and K. alvarezii in the present study.
Gracilaria sp.indicated to be more palatable for gold-mouth turban than Ulva spp.and K. alvarezii.High food intake of Gracilaria sp. also found in abalone H. discus hannai Ino (Qi et al., 2010).Food intake of gold-mouth turban might be influenced by nutritional content of seaweed.Although the nutrition contents of the seaweed were not analyzed in the present study, protein content of Gracilaria sp. have been reported in the range of 11.27 to 21.54% dry matter (Capinpin and Corre, 1996;Viera et al., 2005;Viera et al., 2011).Protein from Gracilaria spp.has also been reported to be effectively utilized by abalone H. tuberculata coccinea Reeve (Qi et al., 2010).Lower protein content in Ulva sp. and K. alvarezii (2.99 and 5.35% dry matter, respectively) (Capinpin and Corre, 1996;Angell et al. 2012) may cause a low effect in the growth rate of T. chrysostomus in this study.
Gold-mouth turban consumed red algae K. alvarezii four times lower than Gracilaria sp.We suspect that feed preference of the snail was also influenced by the degree of toughness of the seaweed.The results of this study were supported by McShane et al. (1994) who found that the toughness of seaweed has a significant influence on food intake of abalone H. rubra, tough seaweed being consumed less than soft seaweed.The low consumption rate of K. alvarezii compared to Gracilaria sp. has also been found in abalone H. asinina (Capinpin and Corre, 1996).
The low food intake of gold-mouth turban fed with Ulva spp. in the present study might be related to the chemical compound of the seaweed.Some species of Ulva have been reported to produce dimethylsulfide (DMS) that could act as feeding deterrents for marine herbivores (Van Alstyne and Houser, 2003;Erickson et al., 2006).However, the percentage of the final weight of gold-mouth turban fed with Ulva spp. was twice as high as snail fed with K. alvarezii.Foster et al. (1999) found that enzyme activity of structural polysaccharide carrageenan was low in the digestive gland of marine gastropod T. sarmaticus fed with red, green and brown algae.In contrast, Rhodophyta K. alvarezii is an excellent source of carrageenan (Hayashi et al., 2007;Hung et al., 2009;Hayashi et al., 2011), and it reflects that low growth performance of T. chrysostomus fed with K. alvarezii might be related to carrageenan content and low enzyme activity.Foster et al. (1999) also showed that digestive enzyme activities of storage polysaccharide of red algae were higher compared to green and brown algae in marine gastropod T. sarmaticus.They demonstrated that digestive enzyme activity in the digestive gland of storage polysaccharide glycogen and amylose were 180.8 and 147.9 (μg -1 ml -1 h -1 ) mg -1 protein, respectively.Foster and Hodgson (1998) reported that apparent dry matter digestibility of red algae Gelidium pristoides and green algae Ulva rigida in T. sarmaticus ranged from 1.06 to 2.32%, and from 2.85 to 8.91%, respectively.It could be assumed that low growth performance of T. chyrsostomus in the present study is due to low apparent dry matter digestibility of red algae K. alvarezii.

CONCLUSION
The present study clearly indicates that seaweed Gracilaria sp. is prospective to be used as a diet for gold-mouth turban (Turbo chrysostomus L., 1758) without negative effect on the growth performance.

Table 1 .
Design for feeding trialprogram at a significant level P<0.05.The Further Tukey test was completed when there were significant differences between trials.