The dolphin fish, or lampuka, only lives for two years at most, according to a study.
More than 4,000 individual dolphin fish from traditional Maltese and modern fishing methods were examined
Data taken from the dorsal spines of adults and ear-bones of juveniles indicated the fish is a short-lived species even when it does not find its way to a Maltese dinner table.
The research was carried out by Mark Gatt for a Master of Science project.
The popular lampuka is one of the most important species for the Maltese fishing industry, amounting to about 30 per cent of the total landings throughout the year.
Biological studies were carried out to get up-to-date information to help manage this resource. More than 4,000 individual dolphin fish caught using traditional Maltese and modern fishing methods were examined during 2004 and 2010.
The fish reached a maximum length of 107.8cm for males and 120.2cm for females in a very short time.
In fact, juveniles were calculated to have an average growth rate of 5.1mm a day.
The relationship between the length and weight showed a significant difference between males and females after reaching sexual maturity.
At a length of 60 to 70 cm, males start developing a bullhead, making them heavier and rounder than females of comparable length.
The length and weight was also used to measure the fish’s well-being. Plump specimens indicate favourable environmental conditions such as good habitat and ample prey.
Lower values were found in adult fish sampled during the winter, spring and summer.
This is most likely related to low metabolic rates and slow growth associated with low water temperatures in winter and with physiological changes due to the high energy demands required during the spring-summer spawning period.
Their condition generally improved in autumn, after the spawning period ended and when water temperatures were still warm enough to permit high meta-bolic rates.
Ear-bones, or otoliths, are calcareous structures found in the inner ear of all bony fish and provide a wealth of scientific data.
Not only does an otolith tell a fish’s age as each day and year of existence is represented by a ring, just like a tree, it also provides very detailed information about its health, habitat and diet.
By counting the number of bands or increments in otolith material in a juvenile dolphin fish, its age in days could be determined.
Otolith readings indicated that dolphin fish spawning occurs from June to September in the central Mediterranean, with peak levels in June.
Knowing the timing of spawning is essential in fisheries management as limiting fishing during this period safeguards stocks in danger of overexploitation.
Mr Gatt’s work also demonstrated that dorsal fin spines have a strong potential for use in aging adult specimens of this species, as the age in years can be calculated by counting the number of bands in the spines’ cross sections.
The work formed part of a study by the Strategic Educational Pathways Scholarships, STEPS, awarded by the Education Ministry in collaboration between the university’s Marine Ecology Research Group and the Fisheries Control Directorate.