Spotted grunter

These popular table fish have long, sloping foreheads with a pointed snout. The dorsal surface of the silvery body is covered with many small brown spots that extend onto the dorsal fins. A distinct black blotch occurs on the serrated gill cover. Spotted grunter prefer the brackish waters of shallow coastal estuaries and lagoons.

These fish can also tolerate fresh water. Spotted grunter are widespread from Cape Point along the whole African and Madagascan coast, into Indian waters. Some species of grunter, including the spotted grunter, are able to make a grunting sound by grinding the strong jaws in their throat together, hence their common name.

CLASSIFICATION

PHYLUM:  Chordata
SUBPHYLUM: Vertebrata
CLASS:  Osteichthyes
ORDER:  Perciformes
FAMILY:  Haemulidae 
GENUS:  Pomadasys 
SPECIES:  commersonnii
COMMON NAME: spotted grunter

 

BREEDING HABITS

Spotted grunter reach sexual maturity in their third year of life when they are 30 - 40cm in length. In South Africa, spawning usually occurs in the open sea adjacent to river mouths, between August and December. After spawning, the newly hatched larvae and the post spawning adults move into estuaries to take advantage of the nutrient rich estuarine waters. The murky waters of estuaries also provide the juveniles with protection from visual predators.

 

FEEDING HABITS

Spotted grunter have an unusual method of feeding. They use the pumping action of their large gill chambers ‘in reverse’ to force a jet of water through their mouths. This jet of water then ‘blows’ small prey such as worms, crabs, mud and sandprawns out of their burrows in the sand. Grunter are often seen with their tails out of the water as they feed, head down, on shallow mud banks. It is often easy to see where a shoal of spotted grunter have been feeding - the sandy bottom is covered by many tiny mounds of sand. Grunter also eat mole crabs (sealice) and small molluscs. Grunter have thick lips surrounding a small mouth bearing several rows of very fine teeth. The tough pharyngeal teeth that are found in the throat area assist in the crushing of their prey.

 

LIFE CYCLE

Spotted grunter reach a maximum length of 87cm at an age of about 15 years, and a weight of 9.5kg. Tag returns have shown that adult fish appear to be fairly resident in the vicinity of estuary mouths.

 

CONSERVATION STATUS

Spotted grunter depend on estuaries for the growth and protection of juveniles, as well as for adult feeding areas. This makes them particularly sensitive to estuarine degradation such as siltation or pollution. Spotted grunter are a very popular angling fish and are commonly caught in estuaries, particularly in the St Lucia estuary, which is famous for its spring grunter run.

Grunter are also caught from sandy beaches and are sometimes caught as a by-catch in prawn trawl nets operating off the Tugela Banks. Spearfishers frequently spear this fish and subsistence net and trap fishers in KwaZulu-Natal also catch large numbers of spotted grunter.

 

WHAT YOU CAN DO TO HELP

There are a limited number of grunter in the ocean. If anglers catch more than can be replaced by their breeding, over-fishing results. This results in fewer grunter and their average size becoming smaller. To prevent this, regulations control the number of grunter that can be caught, ensuring that everyone catches their fair share and that grunter continue to be caught in the future.

Obey fishing regulations

  • Minimum size limits give fish a chance to breed at least once before they are caught and protect the fish when they are growing at their fastest.
  • Bag limits restrict daily catches so that there will be enough fish for everyone. Scientists work out how many fish can be harvested safely. This information is used to set a bag limit that restricts the number of fish caught per day. This prevents more successful anglers from catching large numbers of fish, especially when the fish are ‘on the bite’, so leaving some behind for less successful anglers.
  • Closed seasons protect fish during vulnerable stages in their life cycles.

Where available, fill in catch cards with accurate information about your catches and co-operate with fisheries officers or scientists collecting information on your catch.

When fishing in an estuary in KwaZulu-Natal, please complete the pink catch cards that are available at many launch sites. These provide information about the number of anglers and the number of fish being caught. Scientists can tell the age of fish by counting rings in their ear bones (otoliths) and relating this to the size of the fish. The age that the fish start breeding as well as their breeding season, may be determined by cutting open the fish and inspecting the state of maturity of their reproductive organs. 

Research is also conducted on the diet of the fish. Scientists use all this information in computerised mathematical models to determine the most effective management options. The best options can then be drafted into regulations that are used to manage recreational species such as grunter.

Tag and release your fish

Tagged fish can provide scientists with useful information about the seasonal movements of fish, their growth rates and in some cases, the size of the stock. They also give anglers an opportunity to become involved in an exciting research programme; taggers receive information about their tagged fish, if they are recaptured. If you catch a fish with tag in it, read the tag number or remove the tag from the fish and measure the fish (from the tip of the mouth to the fork of the tail).

Send the tag number (or tag), the type of fish, where it was caught (try to give a specific location), the date caught, the length and/or weight of the fish and your name, address and telephone number to: The Tagging Officer, Oceanographic Research Institute, P.O. Box 736, Durban, 4000.

Only catch what you can eat – don’t be greedy.

 

FURTHER INFORMATION

van der Elst, R.P. 1988. A Guide to the Common Sea Fishes of Southern Africa (2nd ed). Struik Publishers, Cape Town.

Downloadable fact sheet