Introduction
Sustainable growth of the salmon aquaculture industry is highly dependent on the availability of new and locally produced feed resources (Albrektsen et al., 2022, Tacon et al., 2011), and improved approaches to managing and utilizing waste streams from production (Waite et al., 2014, Turchini et al., 2019). Polychaetes can upcycle valuable biomolecules contained in aquaculture sludge and other waste streams (Anglade et al., 2023, Wang et al., 2019a), while at the same time being a potential feed ingredient in aquafeeds (Monteiro et al., 2024, Wang et al., 2019b). Future large-scale production of the polychaete Hediste diversicolor (OF Müller, 1776) will be dependent on extensive knowledge, control, and manipulation of the life cycle of the species (Olive, 1999, Wang, 2020). In this study, the effect of different light and temperature regimes on the maturation and reproductive success of H. diversicolor was evaluated.
Material and methods
Wild collected individuals of H. diversicolor were acclimated under laboratory conditions for two months prior to being transferred to the experimental units in December 2024. A full-factorial experimental design was used, combining two temperature regimes (14°C and a temperature regime of 6-14°C simulating natural temperature variation) with four light regimes (16L:8D, 24L:0D, natural light conditions, accelerated natural light conditions), resulting in seven treatment combinations. Each treatment consisted of four experimental tanks and one reference tank. All groups were fed commercial fish feed twice weekly. In the reference tanks, biweekly sampling was conducted to assess survival, measure individual biomass, document individual condition via photographic analysis, and assess maturation status by extraction of germ cells from a minimum of five individuals per sampling.
After 14 weeks, all remaining were dissected to quantify reproductive output in females through egg counts. At the same time, an exploratory sampling was conducted in the experimental tanks to determine the presence or absence of offspring, with the aim of verifying spawning and reproductive success. Additionally, more comprehensive samplings were scheduled for weeks 20 and 26 to assess later developmental stages and further evaluate reproductive success across treatments.
Preliminary results and discussion
With the progression of maturation, the survival of H. diversicolor decreased across all treatments over time due to its semelparous life history (Hartmann-Schröder et al., 1996). Individuals in the 16L:8D light treatment group, in both natural temperature conditions and at 14°C showed the most rapid decline in survival. Correlating this decline with the onset of reproduction and higher reproductive success in terms of offspring numbers will be crucial for understanding these results, however, this is yet to be evaluated. Variation and light did not affect the final egg mg-1 count (one-way ANOVA, p ≥ 0.05), suggesting no difference in retention of eggs in the coelom.
Conclusion
Overall, the light regime appeared to exert a stronger influence on the maturation of H. diversicolor than temperature, with more detailed results yet to be assessed. These findings may support the development of large-scale production systems by enabling faster maturation and reproduction.
References
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