Saturday, April 7, 2012

Grouper and Groupers

Groupers (class Actinopterygii, order Perciformes, family Serranidae, sub-family Epinephelinae) comprise 14 genera and 449 species of the subfamily Epinephelinae, or roughly half of all species in the family Serranidae (groupers and sea basses). There are 16 major grouper species that are cultured; the dominant species vary somewhat regionally. The most consistently abundant species that are captured for culture purposes and also reared in hatcheries are Epinephelus coioides and E. malabaricus.

Other important species are E. bleekeri, E. akaara, E. awoara and E. areolatus. E. amblycephalus, E. fuscoguttatus, E. lanceolatus, E. sexfasciatus, E. trimaculatus, E. quoyanus, E. bruneus, Cromileptes altivelis, Plectropomus leopardus and P. maculatus are cultured in small amounts. In the southeastern United States of America and the Caribbean, E. striatus, E. itajara, Mycteroperca microlepis and M. bonaci seem to have good farming potential. However, CBA for groupers in the western hemisphere has not been developed to any large extent, unlike in Southeast Asia.

Juveniles and adults of some grouper species live in coastal or lagoonal waters and estuaries, while others prefer the cleaner waters of offshore reefs. Their eggs are single, non-adhesive, and buoyant at normal salinities. The larvae of most species spend about 30–50 days as planktonic larvae. As they become juveniles, groupers settle in shallow waters where they seek shelter in seagrass beds, mangrove prop roots, coral rubble, branching coral or branching macroalgae. Some juvenile groupers are habitat generalists, settling in any available shelter, while other species have specific nursery habitats in which their growth and survival are enhanced. After hatching, wild grouper larvae eat copepods and other small zooplankton. They switch to larger crustaceans, such as amphipods and mysid shrimp, as they grow. Wild juveniles and adults eat fish, crabs, shrimp, lobsters and molluscs, although the genus Plectropomus tends to be predominantly piscivorous.

Groupers range in maximum size from only 12 cm (e.g. Paranthias colonus) to over 3 m (e.g. Epinephelus lanceolatus). Most groupers that have been studied are sexually mature within 2–6 years, but some of the larger species may take longer to mature, e.g. Epinephelus fuscoguttatus, which matures at about 9 years. Most serranids are protogynous hermaphrodites. As a rule, some change from female to male as they grow older; others may change only if there is a shortage of males. In nature, many species spawn in large aggregations (hundreds to thousands of fish) with a sex ratio nearing 1:1. In some cases, several grouper species may share the same aggregation site.

Groupers are some of the top predators on coral reefs, and tend to be K-strategists demonstrating slow growth, late reproduction, large size and long life-spans which make them vulnerable to overexploitation. Also contributing to their vulnerability is the fact that they are sex-changers with a low proportion of males in the smaller cohorts, which means that heavy fishing pressure often removes most of the males (or removes fish before they can become male). Additionally, many groupers form spawning aggregations that are predictable in space and time, making them extremely easy to harvest. These aggregations can represent the entire annual reproductive output for some species. Groupers are sedentary in character and strongly territorial, making them easy targets for spear fisheries.

Groupers are greatly valued for the quality of their flesh, and most species command high market prices. Groupers are the most intensively exploited group in the live fish trade, and the high prices paid by exporters to local fishermen mean that target species may be heavily over-fished. In order to alleviate the pressure on wild grouper stocks, many nations have promoted aquaculture in the hopes of producing a more sustainable grouper yield. However, full-cycle culture of most grouper species is not yet possible, although several important advances have been made in recent years. For this reason, about two-thirds of all grouper culture involves the capture and grow-out of wild seed. This is known as capture-based aquaculture (CBA).

There are at least 16 species of groupers that are cultured in many Southeast Asian countries, including Indonesia, Malaysia, Philippines, Taiwan Province of China, Thailand, China Hong Kong Special Administrative Region (SAR), the southeast of the China and Viet Nam (Sadovy, 2000). Grouper culture is also undertaken in India, Sri Lanka, Saudi Arabia, Republic of Korea, Australia, the Caribbean and in the southeastern United States of America. Despite the huge popularity of live fish in China and Southeast Asia, only 15–20 percent of the amount consumed each year comes from aquaculture, as culture is principally constrained by limited and unreliable supplies of wild seed and the difficulties of spawning in captivity.

Grouper seed is collected using a variety of methods. Capture methods are generally artisanal and the fishermen employ a variety of artificial habitats. Some grouper seed collection methods are more damaging than others. Clearly destructive methods include those that result in high mortality, involve high levels of bycatch, and/or cause damage to the fish habitat. A further problem is that some methods result in monopolization of the local fishery by a few individuals. Destructive methods include scissor nets and fyke nets, which are already banned in some areas. The mortality rates that follow capture and transport are not well documented; estimates for over the first 2 months after harvest are quite variable (30–70 percent), depending on the quality of fry, the level of transport stress, and the presence of disease and cannibalism.

Because full-cycle culture of most grouper species is not yet possible, approximately 66–80 percent of all grouper culture involves the capture and grow-out of wild seed and the volume of seed caught each year exceeds hundreds of millions of individuals. When seed catches are compared to the numbers of marketable fish produced, the results strongly suggest crude and wasteful culture practices. Sadovy (2000) estimated that about 60 million seed fish are needed to produce the regional total of 23 000 tonnes of table-size live fish from culture annually.

Trash fish is commonly used for feeding in grouper cage culture, but its increasing cost, shortage of supply, variable quality and poor feed conversion ratios indicate that this form of feed may not be the best from either a nutritional or an economic point of view. A dependable supply of cost-effective, non-marine, sources of alternative protein must be provided if grouper farming is to remain profitable. Millemena (2002) demonstrated that up to 80 percent of fishmeal protein can be replaced by processed meat meal and blood meal derived from terrestrial animals with no adverse effects on growth, survival, and food conversion ratio (FCR). From an economic standpoint, replacement of fishmeal with cheaper animal by-product meals in practical diets can alleviate the problem of low fishmeal availability and high costs.


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