Influence of Body Weight and Water Temperature on Growth in Ragworm Hediste diversicolor

Abstract

Cultivation of the common ragworm—Hediste diversicolor—has attracted a great deal of interest in recent years. Growth optimization is a key aspect for its intensive production. We have assessed the effect of body weight (Bw) and temperature (T) on growth-related parameters in common ragworm using correlation and multiple regression analyses. We used ragworms of 13 different weight classes in 15-day growing assays at 12 different temperature values. These polychaetes were stocked at a density of 1000 individuals m−2, and fed with commercial fish feed. Our results show that growth increases with T; when expressed as an absolute growth rate (AGR), growth increases as Bw increases; and when expressed as a specific growth rate (SGR), growth decreases as Bw increases. A change in the growth pattern was observed from an individual Bw of about 400 mg. Simulations performed with the equations that provided the best fit revealed that optimum T for growth changes with Bw, so that in individuals below 400 mg, optimum T is 24.9 °C, and above this temperature growth decreases. In individuals above 400 mg, growth increases slightly with temperature, but as weight increases, the effect of temperature on growth is less and less, and from a weight of 1050 mg, growth decreases as temperature increases. Mortality increases significantly at temperatures above 22 °C, especially in individuals with a Bw above 400 mg. Simulations of individual growth showed that up to 400 mg growth is quite fast at warmer temperatures, but from 400 mg to 1000 mg, the influence of T on growth rate is not significantly relevant in operational terms. This study demonstrated the huge usefulness of growth modelling for production planning.

Effects of Rearing Density, Substrate Height, and Feeding Frequency on Growth and Biomass Production of Hediste diversicolor

“…We did not assess reproductive events as no larvae was detected (a possible explanation is the net walls of the culture units might have allowed larvae to escape); however, at day 70, we inspected 33% of the survived worms and found the diameter of the oocytes of surviving females to be 129 ± 39 µ, an advanced stage of maturity according to the literature [9,32]. Our results suggest that time of harvesting is a key factor to attain high production; this represents a compromise between maximizing growth and controlling reproduction, both of which depend on environmental factors, mainly temperature [27] and type of food [9,19].…”

“…The recirculating flow rate in each tray was 1.5 L min −1 . The EUs inside the trays remained partially submerged so that the sediment columns were always immersed but the upper part of the EUs were out of the water, meaning that both the ragworms and the feed supplied were prevented from escaping the experimental units, while allowing water exchange [27].…”