Date

Summer 2023

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

White abalone (Haliotis sorenseni) are an endangered species found along the California coast. They are at historically low densities, nearing extinction. Aquaculture facilities throughout California are currently involved in the captive breeding of the species and grow out of juveniles for outplanting to wild habitat. White abalone have historically suffered from an infectious bacterial disease known as withering syndrome or Ca.Xc. This disease can be treated with an antibiotic, but antibiotic treatments can lower immune functions and create antibiotic resistance genes. A probiotic treatment could replace this need for antibiotics and increase overall health and growth rates in white abalone. White abalone restoration activity aims to enhance the species recovery by developing self-sustaining populations, which is costly due to the species’ slow growth, high early mortality rate, and reliance on seasonal macroalgae feed. These limiting factors warrant an assessment of alternative diets and probiotic treatments 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 can provide adequate nutrition and reduce costs for several cultured species.

The probiotic, Bacillus licheniformis was added to macroalgae feed for white abalone exposed to and unexposed to Ca.Xc. No Ca.Xc was detected in any of the white abalone at the end of the study. This indicated that white abalone may be able to combat Ca.Xc with a bacteriophage (pCXc). Shell loss during the first probiotic experiment hindered data collection on feeding and growth rates. In the first probiotic study 42% of the white abalone and 53% of the red abalone lost their shells. Two subsequent studies were conducted to understand the cause of the shell loss. These studies were inconclusive, but one experiment showed that low stocking density (588 abalone/m2) increased feeding and growth rates compared to high densities (1,176 abalone/m2).

The second probiotic study investigated the effects of B. licheniformis on a formulated abalone feed, ABKelp®. Three diet treatments were assessed: 1) formulated, 2) formulated + probiotic, 3) standard (Devaleraea mollis and Macrocystis pyrifera). The standard treatment resulted in the fastest growth and feed intake. The formulated + probiotic treatment had the lowest growth and feeding rates, which may be due to reduced palatability from the probiotic. Despite comparatively inferior growth metrics, the formulated treatment resulted in adequate growth and survivorship in white abalone. 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 M. pyrifera collection and culture facilities devoted to macroalgae culture and storage. The growth rates, feeding rates, and proximate analysis suggest that formulated feed is not a viable alternative diet for white abalone, but could be used as a supplemental feed for conservation aquaculture facilities with limited access to fresh macroalgae or during times of the year when fresh feed is unavailable.

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