Development of Pacific Threadfin and Milkfish Growout Technology and Production of Live Feeds and Seedstock |
The overall goal of this project is to develop growout technology for Pacific threadfin (Polydactyulus sexfilis) and milkfish (Chanos chanos) and transfer that technology to the aquaculture industry. Specific objectives related to that goal are to:
Objective: Identify suitable commercial facilities in Hawaii for growout of threadfin through on-site growout trials.
Six commercial farms participated in growout trials to evaluate the suitability of various facilities. To replicate results, two runs were scheduled for each farm site at the beginning and end of the natural spawning season. In each trial, farmers were given fish from the same spawn; all farmers gave the fish Moore-Clark mahimahi diet.
A total of 110,000 juvenile threadfin were distributed to six cooperating farms on Oahu and Hawaii. The fish were stocked into either large production tanks or pen facilities in Hawaiian fishponds; target harvest densities were 15 kilograms per cubic meter in growout tanks and 8,000 pounds per acre in pens.
In addition, 4,560 fish were stocked in growout facilities at The Oceanic Institute (OI) and Hawaii Institute of Marine Biology (HIMB) for experiments. At OI, fish were stocked into each of four replicate 10-foot-diameter and 20-foot-diameter tanks at densities of 50 fish per cubic meter and at initial loading rates of 0.1 kilogram per liter per minute water flow. The water flow increased to 1.0 kilogram per liter per minute at the end of the trial to determine the effect of tank size on fish growth and to serve as a growth reference for the commercial facilities. At HIMB, fish were stocked into eight 1.2-cubic-meter pens at either 30 or 60 fish per cubic meter to determine the effect of stocking rate on growth and survival in these systems. Threadfin were sampled at 30-day intervals, and growth and survival rates compared with those raised at OI.
Three farms on the island of Hawaii and one on Oahu received 30-day-old fish. OI staff provided hatchery facility owners with technical assistance regarding setting up the nursery facilities.
Farm results have been encouraging, with overall survival rates of 78 percent. Threadfin have grown well in both brackish water and saltwater conditions. Anecdotal evidence suggests that fish cannot survive for extended periods at salinity below 20 parts per thousand. Nursery survival at farm sites ranged between 50 and 90 percent, while survival in the OI nursery averaged 85 percent. At Day 102, the average weight of fish ranged from 45 to 60 grams at cooperating facilities; the average weight of fish at OI was 64.2 grams at Day 95. The first harvest from this group began in January 1997, when fish were 7 months old. The second rearing was conducted in early November and targeted 50,000 juveniles for distribution. All the farm facilities agreed to replicate the first run.
Results of the HIMB cage experiments indicated no difference in weight gain and specific growth rate between the two stocking densities. However, results should be viewed with caution. Feed conversion ratios and survival rates were poor for both densities, but the fish grew and survived, so this type of environment should be considered in future investigations. Perhaps better results can be achieved with increased supervision and cages built from stronger materials.
Objective: Identify suitable, locally available commercial feeds for threadfin growout.
Based on recommendations from a previous threadfin project, farmers are using a Moore-Clark mahimahi diet for threadfin growout. An experiment was conducted to determine if other commercial feeds would be suitable for threadfin growout at lower feeding costs. Four feeds were tested: Moore-Clark (MC) Threadfin, MC New Age Salmon, Rangen Salmon Grower, and Rangen EXTR 450. Each diet was fed to satiation twice a day to four replicate 1.5-ton tanks (16 tanks total) each stocked with 40 Day-60 fish. Fish were stocked at a mean weight of 9.8 grams and grown to Day 116. Results indicated significant differences in growth and survival of threadfin given the four diets.
An experiment was conducted at OI to determine the effect of both tank size and a Moore-Clark mahimahi diet containing 55 percent protein versus a specially formulated threadfin diet containing 45 percent protein. Four 10-foot- and four 20-foot-diameter tanks were stocked with Day 65 threadfin at a density of 50 fish per cubic meter of working volume. Fish had been fed the mahimahi diet from Day 45 through Day 65. At Day 65, duplicate 10-foot- and 20-foot-diameter tanks were switched to the respective experimental diets. Fish were fed twice daily to satiation. Fish were weighed and measured every 30 days until harvest at Day 180. Results indicated that tank size and percentage of protein significantly affect growth and performance of threadfin.
Based on these results, threadfin should be grown in tanks at least 20 feet in diameter and given a diet of either 45 percent or 55 percent protein to optimize biological performance for threadfin growout.
Objective: Determine the loading rate that promotes optimum growth and feed utilization in threadfin growout.
Costs associated with pumping seawater are the most expensive operating costs for an onshore growout facility. The animals' tolerance limits to un-ionized ammonia determine the biomass of fish that can be raised with a given flow of water. This is termed the "loading rate" and is often measured in kilograms of fish per liter of water flow per minute. Determination of optimum loading rates for threadfin is crucial in assessing economic feasibility of threadfin culture because Hawaii electrical rates are among the highest in the nation.
Four 10-cubic-meter tanks were each stocked with 450 Day 60 threadfin. Duplicate tanks were used for each loading rate treatment. Water flow rates were set to reach target harvest load of 2.0 and 1.0 kilograms per liter per minute at Day 180. Fish were fed twice a day to satiation and measured and weighed monthly. Water samples were taken to determine total ammonia and pH during peak periods of the day prior to each monthly sample. Survival and growth of fish raised to harvest size showed no difference at either loading rate, although total and un-ionized ammonia levels in the high loading rate treatment tanks (2kg/l/m) were always twice that in the standard (1 kg/l/m) loading rate treatment tanks. In fact, those fish raised at 2kg/l/m had a 1.49 feed conversion ratio, which was slightly lower than the 1.60 feed conversion ratio of those fish raised at 1kg/l/m. Threadfin appear to tolerate un-ionized ammonia levels as high as 0.08 ppm quite well for short period of time and 0.04 ppm for longer periods without adverse effects.
Objective: Generate socio-economic and market characteristics of harvested threadfin through sales to distributors and other outlets.
KTA Superstores in Hilo, Hawaii, participated in test marketing 400 total pounds of 0.75-pound threadfin per week in January and February. The store suggested that a 2-pound threadfin would fetch a higher price. To determine the economic feasibility of raising fish to that size, 700 fish were grown 6 additional months in two 20-foot-diameter tanks. The threadfin were fed to satiation twice daily and sampled monthly for weight gain and length. Growth and feed conversion were compared between the two periods of growth. Results indicated that growout to an average 1.5 pounds is feasible within a year, but growth and feed conversion are adversely affected. Growout of threadfin to the larger 1.5- to 2-pound market size increases feed costs by 55 percent and may not be economically feasible for farmers unless premium prices can be obtained.
Fish distributed last year to farmers have already appeared in the market place. Off-the-farm price is $6.50 per pound for 0.75- to 1-pound fish and $2 per pound for a 2- to 3-ounce fish. Cultured threadfin have been sold to Times Supermarket, which has advertised them at $10.99 per pound, to Safeway and Daiei, which have advertised the threadfin for $8.99 per pound and to Rick's Restaurant in San Francisco.
Objective: Identify suitable commercial feeds for milkfish growout and assess its potential as baitfish.
A feeding trial was conducted to determine the suitability of four local commercial fish diets. Sixteen 1.5-ton round fiberglass tanks were stocked with 100 Day 60 milkfish with an average weight of 3 grams. Four replicate tanks of fish were fed twice daily to satiation with either Sunfish Pellet, which cost $0.30 per pound; Catfish pellet, which cost $0.46 per pound; trout pellet, which cost $0.64 per pound, and mahimahi pellet, which cost $0.55 per pound. Fish were weighed at the end of the experiment on Day 116. The results indicated that the mahimahi diet produced the best growth and lowest feeding costs and should be considered when raising milkfish for profit.
Objective: Supply threadfin and milkfish seedstock to commercial farms.
A total of 115,000 threadfin were distributed to five cooperating farms, OI and HIMB. A total of 97,000 Day-40 milkfish were distributed to 15 farms on Oahu, Molokai, Maui and Hawaii. Growout resulted in successful commercial harvests of approximately 58,000 of the fish; another 34,000 are nearing harvest. Market sizes ranged from 0.5 pounds to 2 pounds. Threadfin have grown well in either brackish or salt water conditions in flow-through tanks or pens in Hawaiian fish ponds. Anecdotal evidence suggests that fish cannot survive below 20 ppt salinity for extended periods. Fish grow best at dissolved oxygen levels of 5.0 ppm or higher but reportedly can tolerate oxygen levels as low as 2.0 ppm. Nursery survival at farms ranged between 50 and 90 percent; OI nursery survival averaged 85 percent. Farms have not achieved threadfin growth rates comparable to those attained at OI; however, most farms can produce 0.5-pound threadfin by 6 months of age and 0.75-pound threadfin by 8 months of age.
Milkfish growout trials at farms exhibit an overall survival rate of 63 percent. Approximately 45,000 milkfish, each averaging about 0.75 pounds, remain in growout and will be harvested and sold when they reach 1 pound. Markets for milkfish range from 5 to 6 inches for pan frying to 1 or 2 pounds whole, de-boned for restaurants. Prices average $2.50 to $3.50 per pound for a whole fish.
Objective: Identify cooperating farms and provide ongoing assistance in threadfin and milkfish nursery and growout.
Assistance by OI staff and Sea Grant extension agents has been key to the success of farmers raising these fishes. OI staff and Sea Grant extension agents visited cooperating farms, identified qualified participants and helped them in rearing strategy, facility design, pickup and stocking of seedstock.
Under the previous year of the threadfin fry project and the milkfish project, no technical assistance was provided and only 21,000 of the 150,000 fish distributed reached harvest size. During this project year, technical support helped farmers to achieve threadfin survival rates of 80 percent and milkfish survival rates of 63 percent. Those rates could improve with more education and extension activities for farmers.
Threadfin feeding guides supplied to farmers helped them to maintain rapid fish growth and survival, particularly in the nursery stage. Costs of commercial feed shipments for threadfin were lowered $0.20 per pound by coordinating with a Hawaii company to share a shipping container.
During the second year of this project, investigators will:
Results from commercial farms indicate that farmers can succeed at raising threadfin, given proper guidance. Feeding trials for both threadfin and milkfish aided both in identifying the best commercial feeds and formulations for threadfin growout and in ways to minimize feed costs. Water use costs can also be lowered with the identification of threadfin loading rate requirements. Market tests showed that threadfin ranging from 0.5 pounds to 2 pounds can be sold for $6 to $7 per pound. Threadfin can be grown to 0.5 to 1 pound at 6 to 8 months of age. Given estimated survival rates of fish produced under this project, the average price of $6 per pound in the round and 0.75 pound harvest weight, this CTSA Year 9 project will contribute an estimated $414,000 in net sales to Hawaii threadfin farmers. Total net sales attributed to this project during CTSA Year 8 and Year 9 is estimated at $508,500. Milkfish is in demand as a food product, especially in the Filipino community. Project sales of milkfish from CTSA activities are estimated to be $135,000.
No publications or manuscripts were produced nor were any papers presented during the reporting period.