Distribution of vitamin B12 in bivalve tissues: Investigations of larval and adult lifestages

Abstract

Shellfish, in particular bivalves, are an often-overlooked source of vitamin B12 (B12) in the human diet although they have significantly higher tissue levels of B12 than other animal meat or fish sources, including all vertebrates. However, the origins and key metabolic processes involving B12 in bivalves remain largely unknown. In this study, we examined the distribution of B12 in tissues of several adult Australian bivalve species and assessed hypotheses concerning their B12 utilisation and principal uptake, specifically whether it is derived from diet or gut microbiome. Pacific oysters, Crassostrea gigas, and Goolwa cockles, Plebidonax deltoides (‘pipis’), are both high in B12 (28.0–49.4 μg/100 g total per individual). Vitamin B12 tissue distribution, particularly in oysters, varied significantly, with higher amounts in the adductor muscle (44.0–96.7 μg/100 g), and other tissues, such as gonads, were relatively low (12.7–35.9 μg/100 g). In comparison, concentrations of B12 in the adductor muscle and roe of Southern Australian scallops, Pecten fumatus, were appreciably lower (3.4–10.8 μg/100 g). We also demonstrated that microalgal feed commonly grown in aquaculture can be supplemented directly with B12, resulting in an enriched feed. However, the B12-enriched diet did not transfer to a significant increase in oyster larval B12 concentrations, contradicting our theory that vitamin uptake through feed was a primary B12 source. Vitamin B12 concentrations across oyster larval life stages showed a significant decrease post metamorphosis, which indicates a higher utilisation of B12 during this life event. Our findings also provide insight into B12 uptake and tissue distribution in bivalve species, which can aid the aquaculture industry in promotion of bivalves as a valuable source of dietary B12 for human consumers, while also suggesting ways to optimise vitamin supplementation in bivalve hatchery production.