Locally known as lapu-lapu, grouper has been cultured in ponds and cages in Southeast Asia for more than a decade. It is one of them most expensive fish in the market and is valued because of its texture and taste as well as its great potential in the aquaculture market. The demand of the grouper in the international market is fast growing particularly in Hongkong, Japan, and Singaore.
In the country, grouper culture in cages have been succesful in Pres. Carlos Garcia, Bohol. The Sto. Rosario Fishermen’s Association of this municipality has established market links with buyers based near Cebu City. The Cagay Multi-Purpose Cooperative in Roxas City has also been succesful in culturing grouper. Raising grouper is therefore another significant earner for the country.
There are about 40 species of groupers distributed in tropical water and there are 2 species cultured commercially. These are:
1. Epinephelus coioides or Orange-spotted grouper – They have yellowish-brown dorsal body, shaded to whitish on the side of the belly, and they have numerous brownish orange or brownish-yellow spots unevenly scattered on head, body and fins. Whitish or creamy white chin or underside of the head and belly.
2. Epinephelus malabaricus or Black-spotted grouper – Body color is light brown on the upper part o the body, belly and ventral side light grey. The body has 5 distinct broad dark brown oblique bars which tend to bend. The head and the body with numerous small well-separated blackish spots on the chin. The fins are also has small black spots.
Source of Grouper Stock
At present, supply of grouper fry for commercial cage/pond production still depends on the wild. However, institutes like SEAFDEC/AQD and other progessive finfish hatchery operators are refining their broodstock and production techniques.
Grouper fry are collected in nominal quantities using various devices, eg scare lines or brush piles. The size of fry varies from 1-9 cm and is collected by fish traps from coastal waters near mangrove areas. In the Philippines, the major source of grouper fry are in the provinces of Pangasinan, Cavite, Mindoro, Quezon, Masbate, Bulacan, Cagayan, south Cotabato, and Negros Occidental.
Site Selection for Grouper Cages
The site should:
a. Be in calm water like sheltered lagoons, coves, islets, bay, behind an island or a river mouth. This is to avoid damage caused by strong winds, waves and current.
b. Have salinity ranging between 32-34 ppt
c. Have water depth not less than 3 meters during low tide.
d. Have good water exchange to maintain good water quality
e. Be relatively free from any source of pollution and protected from environmental hazards such as typhoons, floods, erosions, etc. It must be accessible but secured from vandals and poachers.
Grouper Cage Specification
A floating cage is usually composed of 4-12 compartments supported by a framework. Consider the following when putting up a cage:
1. Cage frame – made of bamboo and durable enough to withstand stress caused by wave action and increased weight during culture operation.
Cage dimensions – it should be 5m x 5m x 3m x 3m x 3m x 3m.
2. Maintain water column at 2.5m
3. Sinkers – Use small concrete blocks as sinkers suspended by ropes, placed at the bottom of the 4 corners of the cage for rigging.
4. Catwalks – Attach lumber to the framework to serve as walks.
5. Floaters – Use plastic drums as floaters on each side of the cage between the bamboo pipes. Tie the drum to the cage frame using a rope 5 mm in diameter to stop the drum from drifting, especially during strong wave actions.
Grouper Cage Netting
Nets are placed like an inverted mosquito net or hapa. Each cage is supported with polyethylene rope (5 mm) inserted along the sewed borders of the net and held using a clove hitch with overhand knot.
Each cage should have double-layered nets to avoid loss of stock due to tearing and other mechanical damage.
The rope length from the floater to the anchor should be the same as the water depth at high spring tide. The raft structure needs 14 concrete blocks (0.5 – 1 ton each) with 8 placed at the ebb end (ebb tide being stronger than flood tide), 4 at the flood end and 2 in the mid-section.
Groupers need a place to hide; unlike other fishes. To provide a place for groupers to hide, use sawed-off bamboo, 5 cm in diameter and 15 cm in length (for nursery cages) and 10 cm in diameter and 30 cm in length (for grow-out cages) tied in triangular bundles and suspended in strategic areas inside the net cages.
Grouper Nursery Cage Operation
Use nursery cage for fry 2-10 cm long. Stocking rate should be 60-100 fish per cubic meter. Feeds include shrimps and/or finely chopped trash fish given at the rate of 10% of the average body weight per day. Divide the feeds equally and give 2-4 times each day.
Install a 50-watt incandescent lamp (hover type) inside the cages, about 0.5 m above the waterline at night to attract live food like mysids, copepods, and other smaller fishes.
Grouper Grow-out Cage Operation
Use a grow-out cage to stock sizes of more than 10-15 cm in total length. Stocking rate should be 30-60 fishes per cubic meter. Give trash fish at the rate of 5 percent of the average body weight per day. Divide the feeds equally and give twice a day.
Take a few samples of the stock every 15 days to determine feed requirement and growth rate of grouper stock. Scoop out 10-15 samples and measure the weight and length of each sample. Always inspect the nets for tears. Remove dirt, debris, and fouling organism attached to the nets. Repair or replace damaged nets.
It is recognized that many diseases in fish culture are often associated with stress. Stressed fish can easily be infected with disease-causing agents and this affects growth. The following tips may minimize stress on fish and prevent disease outbreaks:
1. Observe any unusual swimming behavior, especially during dawn or late afternoon. Fish gasping for air usually indicates low levels of dissolved oxygen. Should this happen, thin-out stocks by transferring some of them into another compartment.
2. Weak fish – those refusing to school with other fishes and those losing balance while swimming should be separated from healthy stocks immediately. Stocks found to have sudden loss of appetite and with red spot-like wounds on the skin and fins are likely to have a bacterial infection. Use a Povidone-iodine solution (eg. Betadine solution) at 15 parts per million for 5-10 minutes for 3 alternate days, as an effective treatment for bacterial infection. Methylene blue can also be used by swabbing. Transfer treated fish to a new compartment.
3. Maintain a distance of 1 meter between compartments to ensure easy and continuous water flow and maintain ideal water quality for the fish.
Starve the fish 24 hours before harvesting. Harvest depends on the demand of the local and export market.
Scoop live marketable size groupers (400 g and up) from the cage. Hold grouper temporarily inside the conditioning tank and provide aeration for about 1-2 hours. Adjust water temperature gradually to 18 degrees Celsius by adding packed ice. Place 3-5 fish inside an oxygenated double-sheet plastic bag, with water at 3-5 cm or at least covering the nostrils of the fishes. Place crushed ice on top of plastic bags to maintain the water coolness during transport.
Place plastic bags inside the styrofoam with carton cover having a tag “live fish” and then ready for transport.
Before transporting harvested stocks a “freshwater dip”, or short bath in freshwater for 2-10 minutes is advisable. The dip will not increase parasite infection and lessen the incidence of disease and mortality during transport.
Source:Grouper Culture in Floating Cages BFAR; Livelihood Options for Coastal Communities, IIRR and SMISLE Publication; http://www.pinoyfarmer.com; photo from www.ukdivers.net.