Haliotis midae, commonly known as the South African abalone, is a species of marine gastropod mollusc belonging to the family Haliotidae.
This species is characterized by its ear-shaped shell, which is thick and robust with a row of small respiratory pores along one side. The shell's interior is lined with a lustrous, iridescent layer of nacre, often referred to as mother-of-pearl.
Haliotis midae inhabits rocky shorelines and reefs, primarily in the cool waters off the coast of South Africa. It feeds on macroalgae, particularly kelp, using its radula to graze the substrate.
The species is of significant ecological and economic importance, heavily harvested for its meat and shell, leading to conservation efforts to manage wild populations sustainably.
When Hermanus was founded 150 years ago, perlemoen/abalone was abundant on the shoreline. The fishing industry was the first economic base of the town and became its first tourist attraction as well.
Over the years the bounty of fish was aggressively harvested, many species disappeared and fishers turned their attention to the prized shellfish, abalone. Regulations, limited quotas and limits on the number of packers in the industry could not safeguard the resource. Unfortunately, due to the lucrative international trade in abalone, coupled with domestic political changes, poaching increased to the point that natural stocks were under severe threat
Fortunately, in the 1990's, some entrepreneurial pioneers saw the opportunity to farm this highly-prized species and on-shore farming began in earnest. Research into the spawning and rearing of abalone was in its infancy, but visionaries like Dr Pierre Hugo of Abagold and others, who were prepared to invest time, money and expertise, turned these ventures into a viable farming business.
Today, despite a total ban on sports divers and the complete closure of the commercial harvest, abalone is still in severe danger of being completely depleted.
Systems used in the farming of abalone are recirculating aquaculture systems (RAS), ranching, cage culture and flow-through systems.
The ‘Abalone Feasibility Study’ by Urban-Eco was prepared for the Departement of Agriculture, Forestry and Fisheries (DAFF) in 2018. This study shows cage culture and ranching to be the most profitable systems, but in South Africa, land-based flow-through systems are used.
In these systems, abalone is suspended in baskets in special tanks and fed a specially-formulated diet of artificial abalone feed often combined with fresh seaweed or kelp while seawater is continuously circulated through the system.
In the wild, male and female abalone both release their reproductive cells into the water through small openings. These reproductive cells then connect and fertilisation occurs.
About a day after fertilisation, abalone larvae will hatch and will float in the water for one to two weeks until a good substrate has been found to attach to. The larvae are now called ‘spat’. Over time it will develop a shell and grow by eating micro-organisms, algae and kelp.
Abalone are typically fed a diet that includes:
It's important to note that abalone have specific dietary requirements, and feeding them a varied and nutritious diet is crucial for their health and well-being.
Southern Africa has six endemic abalone species that form a genetically unique cluster inhabiting the coastal waters of South Africa and Mozambique. Of these six species, the South African abalone (Haliotis midae, more commonly known as perlemoen) is the only one of commercial value.
The recently established draft whole genome for H. midae estimates the genome size at 1.5 GB and confirmed the common evolutionary ancestry of South African abalone with the Australian species. The diploid chromosome number of H. midae is 36, with no discernible sex chromosome detected yet. The species, however, do have distinct biological sexes, easily identifiable by observing gonad colour. Lifting the animal’s shell, males normally have light yellow to cream-colored gonads, whilst females have green-colored gonads.
Abalones are broadcast spawners, which normally results in high fecundity and high genetic diversity in abalone populations. The species have a short planktonic larval stage, with dispersal occurring in the natural environment through the action of ocean currents. The retroflection of the Agulhas current at Cape Agulhas creates a barrier for larval dispersal between the west and east coast, restricting gene flow and creating two genetic abalone stocks uniquely adapted to the cool and warm temperate waters on either side of the coast.
The population genetic dynamics of abalone populations are stable on a spatial scale, but they might be much more dynamic over time than previously thought. The high genetic diversity of abalone populations creates a solid base for genetic improvement of the species for aquaculture. Heritability estimates for production traits, like growth, are indeed significant, indicating a strong genetic component underlying these traits, with a number of genes already identified and located on the genetic map of H. midae. Many traits are complex and influenced by both genetic and environmental factors; nonetheless, due to selective breeding for growth, substantial gains in yield have been observed over the last few years.