White abalone (Haliotis sorenseni) are an endangered species found along the California coast and are at historically low densities, nearing extinction. Aquaculture facilities throughout California are currently involved in the captive breeding of the species and growout of juveniles for outplanting to wild habitat. This activity aims to enhance the species recovery by developing self-sustaining populations. However, these efforts are costly because of the species slow growth, high early mortality rate, and reliance on seasonally dependent macroalgae as feed. These limiting factors warrant an assessment of alternative diets and probiotic treatments for the species to shorten the culture time and lower costs before outplanting. Diet administered probiotics have previously shown improved growth rates, feed digestibility, and survivorship in abalone species, while formulated feeds are known to provide adequate nutrition and reduce costs for several cultured species.
This study investigates the effects of a diet administered probiotic (Bacillus licheniformis) paired with a commercial formulated abalone feed (ABKelp® by Algamar) on white abalone. Three diet treatments were assessed in a replicated tank trial: untreated formulated diet, probiotic treated formulated diet and fresh macroalgae diet (Devaleraea mollis ,Macrocystis pyrifera). Live probiotic was cultured and sprayed onto the pellets weekly and stored at 4°C until fed. Feeding rates were measured at every feeding interval, shell length and abalone wet weight were measured individually on a monthly basis. The study was conducted for a total of six months. The fresh macroalgae diet treatment resulted in the greatest growth rate and feed intake (Fig. 1). The formulated diet treated with the probiotic had the lowest feed intake rate, potentially due to a reduced palatability caused by the presence of the probiotic. Despite comparatively inferior growth metrics, the formulated diet treatment still resulted in adequate growth and survivorship in white abalone suggesting it is a viable alternative diet for conservation aquaculture facilities with limited access to fresh marcoalage. The use of a formulated diet is feasible for white abalone restoration aquaculture when considering additional costs associated with fresh macroalgae feeding including, permits, diving, and boat operations for kelp collection as well as culture facilities devoted to macroalgae culture and storage.