Abstract
Calanoid copepods are an important food source for most fish larvae. Their role as a natural prey item means that it is important to develop culture technology for copepods to meet the requirements of larvae culture in aquaculture hatcheries. Copepods have been cultured successfully for some time; however, the implications of long-term cultivation or domestication on copepod life history traits have not yet been assessed. Therefore, the aim of this study was to determine if the domesticated and wild populations of Parvocalanus crassirostris are phenotypically or physiologically different. Wild-caught P. crassirostris were compared to a long-held domesticated strain (>2 years) for size of developmental stage, fecundity and lifespan of adult females, culture density, ingestion rates, faecal pellet production and fatty acid profiles. The domesticated strain was significantly different from the wild strain in size (eggs, nauplii, copepodites and adults were larger in the domesticated strain), egg production (112.3 ± 1.8 eggs female-1 vs. 64.6 ± 3.3 eggs female-1) and adult female lifespan (8.8 ± 0.1 days vs., 7.5 ± 0.1 days). At 1, 3 and 5 adults mL-1, the domesticated strain performed significantly better than the wild strain in egg production (4189.8 ± 61.2, 11224.0 ± 71.7 and 21860.6 ± 103.6 eggs vs. 1319.5 ± 54.3, 2374.5 ± 80.9 and 4933.8 ± 269.5 eggs, respectively) and mean daily mortality rate (5.6% across all densities vs. 22.9 ± 1.6, 29.8 ± 1.2 and 31.3 ± 1.3%, respectively). The domesticated strain had significantly higher ingestion rates than the wild stain (888.4 ± 9.9 ng C l-1 and 775.3 ± 11.2 ng C l-1, respectively), while faecal pellet production was not significantly different between strains. Fatty acid profiles indicated higher levels (as % of total fatty acid) of long-chain polyunsaturated fatty acids in the domesticated strain (36.2±0.4%) than the wild strain (16.1±0.1%). Overall, this study found that the reproductive capacity and tolerance to the culture environment of the calanoid P. crassirostris have improved significantly due to domestication.
Highlights
For the past three decades, there has been continuing interest in the development of mass culture techniques for copepods to be used as live food in aquaculture [1,2,3,4]
The present study is the first to investigate the effects of domestication on the calanoid copepod P. crassirostris after 2 years of continuous culture
Domestication often leads to improved adaptability to culture environments of cultured species and the enhancement of traits related to culture productivity [36]
Summary
For the past three decades, there has been continuing interest in the development of mass culture techniques for copepods to be used as live food in aquaculture [1,2,3,4]. Copepods are the most common metazoans in the marine environment [5], with approximately 11,500 described species [6, 7]. The small size of copepod nauplii is vital for the first larval feeding of various fish species with small mouth gape sizes, such as groupers and snappers [4, 10]. Utilisation of copepods in aquaculture hatcheries is still sporadic, which is largely attributed to difficulties in their culture and, in particular, their low culture productivity [14]
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