The size of the commercial farms under study ranged from 92 to 112 cages with the exception of Respondent F who had 48 cages. These culturists started in their first year of culture with less cages until they gained confidence and reinvested their returns in building more cages. Most of the cages were fully stocked with grouper and sea bass; the local golden snapper was also cultured by all the respondents with the exception of Respondent B. However, the red snapper was cultured only by Respondent A. (Refer to Table 2)
Each farm had one working platform which also served as the night guard house and store for the equipment and nets. The working flatform of the Bukit Tambun farms were wooden houses floated with used plastic drums. On the other hand, the Penang east coast farms were either similar to the floating houses of the Bukit Tambun farms or wooden houses on stilts linked to the land by a jetty.
| Locality | Bukit Tambun | Penang east coast | ||||||
| Respondent | A | B | C | D | E | F | ||
| 1. | Year of Commencement of Culture | 1981 | 1983 | 1982 | 1979 | 1961 | 1981 | |
| 2. | Number Of Cages By Fish Species | |||||||
| 2.1 | Grouper | 25 | 30 | 22 | 24 | 53 | 5 | |
| 2.2 | Seabass | 73 | 78 | 61 | 76 | 2 | 16 | |
| 2.3 | Golden Snapper | 10 | - | 9 | 8 | 53 | 27 | |
| 2.4 | Red Snapper | 4 | - | - | - | - | - | |
| 3. | Total Number of Cages | 112 | 108 | 92 | 108 | 108 | 48 | |
All the cage culturists had cages of size 2.4m by 2.4m by 1.8m with 4 cages per raft. Respondent E had 32 cages of size 1.8m by 1.8m by 1.8m with 8 cages per raft.
Photo 1: A floating platform in the Bukit Tambun cage culture farm served as a working shed, store and night guard house. There were lighting facilities and a television for entertainment.
Photo 2 : A platform on stilts in the Penang east coast farm. The platform was linked to the land by a wooden jetty.
Photo 3 : A commercial fish cage culture farm in Bukit Tambun.
Photo 4: A commercial fish cage culture farm in Penang east coast.
The wooden frame was either of Chengal Batu or Chengal Pasir which was the more hardy wood, placed at the frontal periphery of the farm facing the tidal current. The central cages of the Bukit Tambun culturists were made of the less expensive wood namely Meranti Minyak. The cross sections of the main frame were 5.1cm by 15.3cm, 6.1cm by 7.6cm and 7.6cm by 12.7cm.
All the floats used by the commercial culturists were second-hand ultra-violet light stabilized plastic of suitable thickness and capacity of seven gallons. The economic life ranged from 1 to 5 years. A 6.1m2 raft required 70 to 84 such floats. When the floats were broken, they were replaced while the cages were in use.
All the anchors were either Bakau or Chengal which were completely driven into the mud to prevent destruction by marine borers. Owing to the differences in water depth, the anchor lines of polyethylene rope for the Bukit Tambun cages were from 30 to 40 fathoms (55 to 73 metres) and the anchor lines for the Penang east coast cages were 10 fathoms (18 metres).
All the nets used were polyethylene. With proper care, cleaning and repair, the economic life of the nets ranged from two to five years. The small mesh size net of less than 2.4cm fouled more rapidly but was cleaned more frequently. This net was used only in nursing fingerlings at a size of 2.4cm to 7.3cm and when the fish had grown, the nets were stored and thus last longer and were relatively less used.
| Size (TL) of Fingerlings (cm) | Mesh Size (cm) | Number of ply |
5 – 10 | 0.7 – 1.5 | 6 – 15 |
10 – 15 | 1.5 – 3.8 | 15 – 24 |
15 and above | 3.8 – 5.0 | 38 – 48 |
The cage nets were cleaned everyday and all the respondents emphasized on the urgent need to clean the nets regularly to prevent excessive fouling that may result in net breakage and heavy losses of fish. The smaller the mesh size, the heavier the rate of fouling. The small mesh size nets of less than 2.5cm were cleaned within 1 or 2 weeks of use whereas the larger size nets in 30 to 90 days. The Bukit Tambun culturists' average period of use was 20 to 40 days while for the Penang east coast culturists, it was 60 to 90 days. This difference was basically due to the fouling rate of the different localities.
The method of cleaning involved fish transfer, drying the nets for about 2 days, hitting or spraying to remove the dead fouling agents, dipping in sea water for a day, inspection, mending and finally storage away from vermins especially rats. When nets were to be used, care was taken to ensure that there were no loose knots or holes in the net which would allow the fish to escape.
All the Bukit Tambun culturists were satisfied with the present design of the cages. However the Penang east coast culturists were more adventurous and were working on new designs.
None of the respondents used suspended tyres as ‘fish hide’ to increase the fish stocking density because the tyres might break from the attachment. If this happened, the rhythmic wave action would cause abrasion of nets with the fouled tyres thus resulting in the net breakage and the loss of entire fish stock.
All the culturists did not encounter the problem of fingerling supply because of their established contacts with the suppliers. They were experienced in identifying the quality of fingerlings and paid the supplier accordingly.
The average length of fingerlings cultured ranged between 5.1cm and 20.3cm for grouper, 3.8cm to 10.2cm for sea bass, 5.1cm to 15.3cm for golden snapper and 5.1cm to 7.6cm for the red snapper. (see Table 4)
Photo 5: The cage-nets were periodically sundried and the fouling organisms like bivalves and barnacles were removed by the workers. This was a group duty in the Bukit Tambun fish culture farm.
Photo 6: The culturists supplemented their fish stock with grouper and golden snapper fingerlings caught with a fish trap or ‘babu’. The fishtrap consisted of a bamboo frame covered with nettings.
| Length (cm) | 3.8 – 5.1 | 5.1–7.6 | 7.6–10.1 | 10.1– 15.2 | 15.2– 20.3 | Price by Weight |
| Species | ||||||
| Grouper | - | 1.10 to 1.20 (Ph) | 1.50(Lc) | 2.50 to 3.00(Lc) | 3.20 to 3.30 (Th) | $11.00 /kg.(Lc) |
| 2.40 to 2.50(Th) | 3.00 (Th) | |||||
| Sea bass | 0.50 to 0.60 (Th) | 1.10 to 1.30 (Th) | 1.50 to 1.60 (Th) | - | - | |
| Golden Snapper | - | 0.40 (Lc) | 0.60 (Lc) | 0.60 (Lc) | 0.80 (Lc) | $4.50/ 600g to $6.50/kg (Lc) |
| Red Snapper | - | 1.20 (Lc) |
Sources code: (Ph) = Philippines, (Th) = Thailand and (Lc) = Local
All prices are quoted at C & F during the season of supply.
Fish fingerlings of length 7.6cm to 20.3cm required more care and attention because the frequency of daily feeding was higher and the small mesh size net of 0.7cm to 1.5cm fouled more rapidly resulting in the increase in frequency of net change every one or two weeks. However the stocking density was higher i.e. 80 to 100 pieces per m3 compared to 60 pieces per m3 for fish of the medium class range of 20 to 30cm.
All the culturists also acquired fingerlings on their own using fish traps. The culturists especially in Penang east coast, also purchased locally caught fingerlings and marketable size grouper and golden snapper from fishermen who caught them using fish traps, beach seine nets (pukat kisa) and line. The turn-over of larger fish was relatively more rapid.
All the culturists did not attempt nursing of sea bass fry of length ranging from 1.3cm to 3.8cm in nursery cages because of previous failures by other culturists. However, one culturist attempted nursing of sea bass fry in earthen ponds for 40 days and the resulting survival rate was a mere 48; the initial stocking density being 17,000 pieces per acre.
 | Photo 7: The fish fingerlings had to be periodically graded Careful handling reduced injury and mortality of the fish in the process of transferring. |
 | Photo 8: The large fish to be sold had to be graded to ensure that their sizes were even. A wooden pole seperated the cage-net into two halves and transfer was by use of scoop nets. |
Fish grading during cage culture was practised by all the culturists. The small fingerlings of 5.1cm to 10.2cm were graded as frequent as once per week. Larger fishes were graded once a month. The fish were also graded during marketing to ensure that the size of fish to be sold was the same.
Two respondents did not note any significant species differences in the survival rate of grouper and sea bass provided the fish size was 13cm or more. However, two other respondents from the two localities reported a higher survival rate for the sea bass, 70–80% for initial size of 10.2cm to 12.7cm. They were among the three respondents who reported a lower survival rate for the grouper (50–60%) of initial size of 15.3cm. The local golden snapper of size less than 15.3 cm registered a high mortality rate but when conditioned and recovered from the capture stress, the survival was as high as 80% for the large golden snapper exceeding 13 cm long. The red snapper had more than 90% survival rate but because of the limited availability of fingerlings, coupled with the low demand in the market only one of the six respondents cultured this specie.
All cage culturists experienced fish diseases of red-boil, white spot, swim bladder malfunction and other diseases of yet unknown origin. However, the prevention of diseases was ensured by proper net cleanings to allow free water exchange in and out of the cage nets, giving fresh trash fish and separation of the diseased fish from the healthy ones. Medical swap on the injured area, prophylactic bath, injection of the caudal peduncle of the large fish and medicine incorporated into the feed were practised by some of the culturists. The Penang east coast area, especially Jelutong, experienced sewage run off which aggravated the epidemic of diseases particularly the red boil disease.
All the respondents did not treat the fish fingerlings prior to stocking, because according to them, they did not want to further stress the fish. Prophylactic treatment was administered at least one to two days after the initial stocking, if necessary.
The culture period of grouper and sea bass from 10.2 cm to marketable size ranged from seven months to a year. Although the Bukit Tambun culturists did not report any difference between grouper and sea bass, the Penang east coast reported a longer average culture period of one year for sea bass as compared with grouper of seven to ten months.
The culture period for the two species of snapper ranged from eight to ten months for the fingerlings of initial size of 10.2cm.
One important factor affecting growth rate and the length of the culture period was the stocking density. The stocking densities practised by the respondents are as in Table 5.
| Locality | Bukit Tambun | Penang east coast | |||||
| Cage Size (m) | Respondent Fish Size TL (cm) | A | B | C | D | E | F |
| 1.2×1.2×1.0 | <5.1 | - | 2000 (<10d) | - | - | - | - |
| 1.2×1.2×1.0 | 5.1 – 10.2 | 600–700 (30d) | - | 400–1000 | 500–600 | 350–550 | 400–500 |
| 2.4×2.4×1.8 | 10.2 – 15.2 | 500–600 (30d) | 1000 (15d) | 300–500 | 500 | 350–500 | 400–500 |
| 2.4×2.4×1.8 | 15.2 – 25.4 | 400–500 | 400–450 | 300–400 | 300–400 | 250–350 | 300 |
| 2.4×2.4×1.8 | 25.4 – 35.6 | 200–300 | 300–400 | 200–300 | 300–400 | 200–300 | 200–300 |
Note: (30d) = 30 days in the net
The stocking densities of the Bukit Tambun cages were relatively higher than those of the Penang east coast cages because of better water quality of the former locality.
It was noted that stocking of 1000 to 2000 fingerlings were confined to fish of 5.1 cm to 10.2 cm range in 1.2x1.2x1.0 meter cages and such high stocking rates were for temporary period of not more than 10 days. This was followed immediately by grading and the stocking rate was reduced. A low stocking rate reduced cannibalism of these small size fish.
Respondents A and D reported stocking of two species in a cage as follows:
| Fish Species | Range of Stocking Density (fishes per cage) |
| grouper and golden snapper | 300–400 and 100–200 |
| grouper and sea bass | 300–400 and 100–200 |
This practice was aimed at utilising to the maximum the space within the cages. The grouper was normally sedentary on the cage and the snapper and sea bass were perpetually swimming in the cage midwater.
By this method, a higher stocking density can be practised. However Respondent D noted that during feeding, the grouper, being more aggressive, took the feed first before the snapper or sea bass and the grouper showed a better growth rate. Thus to ensure even feeding, the method of giving feed should be a little at a time. Most culturists did not practise multispecies culture because of the extra effort required to separate the two species especially during marketing of only one specie. Other species in the same net were disturbed.
The production of the respondents ranged from 12.3kg/m3/year to 22.0kg/m3/year and averaged 17.7kg/m3/year. This indicates a stocking density range of 20.5 fish/m3 to 43.7 fish/m3 and averaged 30.4 fish/m3 for the marketable fish. This overall farm performance was based on a year's production as equivalent to one culture cycle and a standardised growth rate for all the fish species cultured as indicated in Table 6.
All the culturists used trash fish which included a variety of marine fishes such as the clupeids or sardines (Clupea spp.) mackerals (Caranx spp.) anchovies (Engraulis spp.) mullet (Mugil spp.) cat fish (Tachysurus spp.) jew fish (Pseudosciaena spp.), lizard fish (Saurida spp.) squids and manthis shrimp. The sardines were preferred because of the relatively lower bone weight.
The sources of trash fish for the Bukit Tambun culturists were the localised wholesale markets in Bukit Mertajam and in Gula. The price ranged from M$0.19 to M$0.20 per 600g ex-Bukit Tambun Jetty. Sources of trash fish for the Penang east coast culturists were Batu Maung trawlers and the local wholesale market, and the prices ranged from M$0.10 to M$0.15 per 600g. No alternative feed was used because of the present low price of trash fish and the convenience in obtaining them.
The frequency of feeding was three times per day for fish less than 12.7cm and up to once in two days for fish that had reached 500g. The Jelutong culturists fed their fish twice a day; in the morning and in the evening. The amounts are presented in Table 7.
| Stocking Density | Fish Size (TL) (cm) | Weight of Feed Per Day (kilo) |
| 300–700 | 5–13 | 1.0–2.4 |
| 500–600 | 13–20 | 3–3.6 |
| 400 | 20–25 | 6–9 |
| 300–400 | 25 – 35 | 6 – 9 |
The Bukit Tambun culturists faced trash fish supply problem for 2 to 5 days in a month although they were not consecutive. The Penang east coast culturists similarly faced trash fish shortage of 3 to 4 days per month and one respondent reported a month of 10 days without trash fish.
The culturists preserved their trash fish in ice when there was an excess or when informed of no supply the following day. One culturist even had a freezer to keep their trash fish for about five days. This was necessary especially during the festival season. They were aware of the necessity to feed the fish fingerlings of less than 12.7cm at least once per day.
The trash fish supplemented the natural food in the form of fish (clupeid) and prawn (Acetes sp) that entered the cages in shoals.
The Feed Conversion Ratio ranged from 1:4.9 to 1:10.1 as in Table 8. The high Feed Conversion Ratio of 1:10.1 is indicative of a relatively poorer performance of Respondent C who also recorded problems of theft, net damage fish loss, and pollution in 1983 at the river mouth. Respondent B exceptional food conversion ration was due to optimal feeding techniques.
| Locality | Bukit Tambun | Penang east coast | ||||
| Respondent | A | B | C | D | E | F |
| 1. Total weight of trashfish consumed (kg) | 145,500 | 109,000 | 109,000 | 129,600 | 79,400 | 43,200 |
| 2. Total sales (kg) | 20,047 | 23,889 | 12,208 | 21,942 | 15,633 | 6,115 |
| 3. Total weight gain (kg) | 18,687 | 22,269 | 10,768 | 20,452 | 14,593 | 5,705 |
| 4. Feed conversion | 7.8 | 4.9 | 10.1 | 6.3 | 5.4 | 7.6 |
All the Bukit Tambun culturists had not heard of growth promoting hormone and the Penang east coast culturists who had helped the research team of USM to prepare the pellet with the hormone as one of the ingredients, did not adopt the method because of the higher cost of the pellet as compared to trash fish.
Photo 9: Feed preparation involved chopping the trash fish. It is recommended that this operation be mechanised.
Photo 10: The cages were constantly guarded by dogs which deterred poachers and sea otters.
