1 NOVEMBER 1999
The marine grouper species are considered high value food fish in several countries. However, controlled breeding and hatchery production of grouper fingerlings for commercial farming is still in its infancy. Investigations on the growth performance of the brown marbled grouper Epinephelus fuscoguttatus (Forskal), camouflage grouper E. polyphekadion (Bleeker) and their hybrid (E. fuscoguttatus x E. polyphekadion) under hatchery and growout culture conditions indicate the potential of grouper hybrids for aquaculture.
Productive studies undertaken at the Fish Farming Centre in the Kingdom of Saudi Arabia indicate that the brown marbled grouper grows significantly faster than the camouflage grouper under hatchery and growout culture conditions. However, the camouflage grouper is more resistant to environmental stress and disease compared to the brown marbled grouper, especially under hatchery conditions (personal observation).
The broodstock of E. fuscoguttatus and E. polyphekadion used for breeding were collected from the hypersaline waters (42% salinity) of the Red Sea coast near Jeddah using handlines and fish traps locally known as gargoor or saquwa during 1994-95. The individual size of broodstock of E. polyphekadion ranged from 3-5 kg and that of E. fuscoguttatus ranged from 12-16 kg. Breeding and larval rearing of these species were carried out using the method described by James et al. (1997). For cross breeding purposes, large size males (about 5 kg) of E. polyphekadion and females (about 12 kg) of E. fuscoguttatus were used. These species exhibited a typical lunar spawning rhythm as natural spawning occurs once in a month in the Red Sea. For cross breeding, the females of E. fuscoguttatus and the males of E. polyphekadion were maintained separately in fiberglass tanks of 25 m^3 capacity with a water depth of 2 m at a stocking rate of 1-2 kg/m^3. The water in the tanks was changed at about 500% turnover in a day. The broodstocks were fed daily to satiation with sardines enriched with cod liver oil by injecting 1 ml of the commercial product 'Seven Seas' into the gut of each sardine before offering them as feed for the broodstock. After confirmation of the gonadal development in females, male fish were introduced in the tank two days before the new moon phase. The spawning took place immediately after the new moon and lasted for three days. It was possible to obtain about 700 000-800 000 eggs per fish per spawning. About 71% of the eggs obtained from each spawning were good quality buoyant eggs. Fertilization was up to 96% and hatching averaged 80%.
After nursing E. fuscoguttatus and the hybrid for 90 days and E. polyphekadion for 120 days, investigations to assess growth of the two species and the hybrid under land based growout culture conditions were undertaken using round fiberglass outdoor tanks (3 m diameter x 1.4 m depth x 10 m^3 working volume). The water was changed about five times per day in the flow-through tank culture system. For comparative growth analysis, the data obtained from a stocking density of 15 fish/m^3 in replicate was used. Locally formulated 4.5-6 mm size moist pellet feed with 40.9% crude protein was used for feeding in the morning and trash fish, composed mainly of Herklotsichthys spp., was used for feeding in the evening. The feed ration amounted to 5% of body weight during the first three months, 3% during the 4-6 months of the culture period and 2% from 7 months onwards until harvest. The fish were sampled monthly for growth monitoring.
The water quality was monitored daily. The water temperature ranged from 28-29 C and salinity 42-43%.
The size of the newly hatched larvae of the hybrid (E. fuscoguttatus female x E. polyphekadion male) ranged from 1.67-1.81 mm, which is smaller than that of E. fuscoguttatus (1.83-1.93 mm) and larger than that of E. polyphekadion (1.55-1.71). Although the newly hatched larvae of E. polyphekadion were smaller in size compared to those of E. fuscoguttatus and the hybrid, they grew rapidly to the size of others, within the first day after hatching. No significant difference (P>0.05) in growth was observed during the early part of the larval rearing up to day 20 between the grouper hybrid and the parent fish species. The hybrid and E. fuscoguttatus larvae grew faster compared to E. polyphekadion 25 days after larval rearing period. On day 35, the size of the hybrid averaged 21.50 +/- 0.629 mm of E. fuscoguttatus 18.80 +/-1.578 and of E. polyphekadion 15.80 +/- 1.166 mm. After 35 days of rearing, growth of the hybrid was significantly faster (P<0.01) compared to the two parents. Also during this period (after day 35) the growth of E. fuscoguttatus larvae was significantly faster (P<0.01) than that of E. polyphekadion. It was possible to obtain about 3 cm size grouper hybrid fingerlings for stocking in the nursery facility at the end of 40 days of larval rearing, whereas it took 45 days in the case of E. fuscoguttatus and 50 days for E. polyphekadion. The fast growth and metamorphosis of the hybrid compared to the parents and other grouper species (Hussain and Higuchi 1980; Maneewong et al. 1986; Al-Abdul-Elah et al. 1996) is of great advantage for commercial applications since it could save considerable space, time and manpower utilization.
Under similar growout culture conditions, a significantly faster growth rate (P<0.01) was observed in E. fuscoguttatus and in the hybrid compared to that of E. polyphekadion. The difference in the hybrid and E. fuscoguttatus was not statistically significant (P>0.05) during the first five months of the growout culture period. However, the higher growth observed in the case of hybrid as compared with that of E. fuscoguttatus during the sixth month of the culture period was statistically significant (P<0.05). Highly significant difference in growth rate (P<0.01) of the hybrid compared to that of E. fuscoguttatus was observed on the seventh month of the growout. It was possible to achieve marketable size hybrid grouper (mean size 695.8 +/- 15.20 g) and E. fuscoguttatus (mean size 598.0 +/- 36.00 g) at the end of the seven month growout period. Whereas, it took about 12 months of rearing for E. polyphekadion to attain a marketable size of 529.4 +/- 28.64 g. Irrespective of initial stocking size, an average daily growth rate of 3.02 g/fish/day was observed in the grouper hybrid, whereas the daily growth rate averaged 2.34 g/fish/day for E. fuscoguttatus and 1.31 g/fish/day for E. polyphekadion.
(Abstract and excerpts from article by C.M. James, S.A. AL-Thobaiti, B.M. Rasem, M.H. Carlos in Naga, The ICLARM Quarterly, Vol. 22, No. 1: 19-23, Jan-Mar 1999)