INFLUENCE OF TAURINE ON LARVAL EYE DEVELOPMENT AND GROWTH PERFORMANCE OF GOLDEN RABBITFISH (Siganus guttatus)

ARTICLE HIGLIGHTS
- Taurine improves eye development in golden rabbitfish larvae
- Enhanced growth performance with taurine-enriched rotifers
- Taurine positively impacts fish eye and body growth

ABSTRACT
Golden rabbitfish (Siganus guttatus) is an emerging species for aquaculture industry, despite constrains faced on commercial scale of seed production due to the high mortality during the first-feeding stage. An experiment was conducted to determine the effect of taurine through enrichment of rotifers as live-feed on eye development and growth performance of larval golden rabbitfish. Observation of eye development was carried out by measuring eye diameter of the larva and development of the retina based on histology assessment. Growth performance was measured for absolute growth and fin development of the larvae and survival rate. The results showed that taurine-enriched rotifer generally provided better performances for eye development and growth of larval golden rabbitfish compared with control (without taurine). Increase of taurine dose up to 0.050 g/L resulted in an increase of eye diameter, absolute growth, fin development and survival rate. Further increased increment of the taurine tended to decrease the values of the measured parameters. The eye diameter of larval golden rabbitfish fed with 0.050 g/L taurine-enriched rotifer was significantly wider (106.1±9.8 µm) (P < 0.05) compared with control (58.2±14.3 µm), but did not significantly differ from other doses of taurine (P > 0.05). Body width of larvae fed with 0.050 g/L taurine-enriched rotifer was significantly higher (127.3±14.6 µm) (P < 0.05) compared with control (98.8±18.3 µm). In regard to eye development, growth performances (total length, fin development and survival rate), dose of taurine for rotifer enrichment fed to larval golden rabbitfish Siganus guttatus was 0.050 g/L.

INTRODUCTION

Siganids or rabbitfish comprise many species, one of which is Siganus guttatus also called golden rabbitfish with local name baronang emas(Laining et al., 2021). Distribution of rabbitfish is mainly in tropical coastal waters. Production of the species is reported different based on the region. In Abu Dhabi-United Arab Emirates, S. canaliculatus was reported to be 149 tons in 2002 from capture(Grandcourt et al., 2007). The Philippines reported production of siganid reaching 150.89 tons in 2005 and increased significantly 45% in 2014(Gonzales et al., 2018). Production from aquaculture was reported in the Philippines since 2018 both from ponds and floating cages culture(Caballero et al., 2022). Indonesia also reported production of siganids which are mainly from capture. Demand of rabbitfish is reported in many parts of Indonesia, in particular in South Sulawesi Province, where fish are commonly served in restaurants and become a typical culinary in the region(Laining et al., 2017). South Sulawesi Province reported production of 3,658.2 tonnes in 2018 and increased 37% in 2021 (https://dkp.sulselprov.go.id/page/info_berkala/kategori/24). Despite demand for rabbitfish, supply from aquaculture has yet met the demand so far.

One major constraint of golden rabbitfish culture is the unavailability of commercial scale seed production. Mortality rate of larvae is still quite high, reaching 50-90% at the age of 2-3 DAH (Days After Hatch), the time where transition period from endogenous nutrition to feeding on life-feed(Rao, 2003). Survival rate during the first feeding stage of golden rabbitfish ranges from 0.2-31.6%(Juario et al., 1985), and survival rate of golden rabbitfish larvae was only 1%. It is argued that failures in the seed production might be caused by the feeding ineffectiveness during the early hatched stage, due to the limited eye sight of the larvae to see the feed. Golden rabbitfish demonstrates a slow growth pattern from their early life to their young juvenile period(Duray, 1998). The eyes were formed on the first day, yet they were not fully developed(Juario et al., 1985). After 1 DAH, the eyes acquire pigmentation and become more pronounced at the age of 2 DAH(Darsiani et al., 2022).

Differentiation of eye is essential for larvae to see and catch the feed(Yufera et al., 2014). One of the contributing factors in the development of larval eyes is nutrition(Stuart, 2013). The nutrition requires enrichment technique to deliver certain nutrient to support the eye. Taurine-enriched feed has been reported to have positive effects on eye, brain, and muscle development (growth) in turbot fish Scophthalmus maximus(Qi et al., 2012). Taurine is a simple protein that is easily absorbed by the body, to support the fish growth(Jusadi et al., 2012). Taurine also improves survival and development of white shrimp during the larval stages(Jusadi et al., 2011), enhances the immune system and reduces stress in zebrafish(, 2019)and contributes in regulating calcium metabolism, including the inside of the eye(Lombardini, 1983);(Lombardini, 1991).

Studies on the taurine-enriched feed has been conducted on various fish, both freshwater and marine species ((El-Sayyed, 2013);(Hernandez et al., 2018)) and reported that marine fish have less ability to synthesize taurine(El-Sayyed, 2013). Effects of taurine are different among fish depending on species, size, and nutritional content of the feed provided and ability of species to synthesize taurine with the help of enzyme CSD (cysteinesulphinate decarboxylase)(El-Sayyed, 2013). This study aimed to evaluate the effect of different levels of taurine through rotifers enrichment on eye development and growth performances of larval golden rabbitfish S. guttatus.

MATERIALS AND METHODS

Experimental Design

This study was conducted at the Rabbitfish Hatchery Instalation of Research Institute for Coastal Aquaculture and Fisheries Extension (RICAFE) in Barru District, South Sulawesi. This experiment was designed in a Completely Randomized Design consisting of 4 treatments with 3 replications. The treatments were rotifers enriched with different doses of taurine, i.e., without taurine enrichment (T 0); with 0.025 g/L taurine dose (T 0.025); with 0.050 g/L taurine dose (T 0.050); and with 0.075 g/L taurine dose (T 0.075) following protocols developed by(Jusadi et al., 2012).

Enrichment of Rotifer

Rotifers type S (Brachionus rotundiformis) harvested from mass culture tank with a density of 500-1,000 ind./mL(Jusadi et al., 2015)were enriched before being given to larvae. Enrichment was performed by preparing 10 L media, requiring 0.5 mL of fish oil A1 DHA Selco, 0.1 g of egg yolk, 0.25 of bread yeast, and taurine PA Sigma which were added according to the respective treatment doses. Taurine and other enriching materials were mixed up with 200 mL water and emulsified using a blender for three to five minutes, then poured into rotifers containers. The enriched rotifers were incubated for 2 hours and harvested by using a 50 µm plankton net then fed to the larvae(Jusadi et al., 2012).

Condition of Larval Rearing

Feeding trial was conducted by rearing larval in concrete tank with capacity of 6 T filled up with 3.5 T of seawater with 20-25 ppt salinity(Lante & Muslimin, 2012). Water was sterilized using UV light (Yamano UV-30W) for 6 hours. During the larval rearing period, green water system was applied by adding Nannochloropsis sp., and maintained at a density of 1x10⁵individual/mL(Duray & Juario, 1988). Newly-hatched larvae (1 DAH) were carefully

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