Improving the fitness of Holothuria arguinensis larvae through different microalgae diets

Abstract

Development and design of adequate feeding protocols on sea cucumber larvae are necessary for improvements on larvae growth, survival and production of competent juveniles. This work assessed the Holothuria arguinensis larvae growth and survival, fed with three different single microalgae diets of Chaetoceros calcitrans, Isochrysis galbana and Tetraselmis chui, and two microalgae diets based on a combination of C. calcitrans and T. chuii (C:T; 1:1) and C. calcitrans, T. chuii and I. galbana (C:T:I; 1:1:1) during 2 months. Holothuria arguinensis larvae fed with T:C:I, showed higher survival and larger larval and stomach sizes than the ones fed with the other diets. Comparing the results obtained from the single diets, H. arguinensis larvae fed with I. galbana grew and survived better during the first 5 days. However, higher growth was obtained on the larvae fed with C. calcitrans from day 5 to day 12; since this day, larvae fed with T. chuii showed the largest size. These results could be related to the different microalgae size and morphology, in addition to the nutritional value of the different microalgae used. However, no competent larvae that metamorphosed into doliolaria were obtained during this experiment. The tanks used were transparent, which could be causing light stress to the larvae, since competent larvae were obtained in opaque production tanks in our aquaculture installations during the same time period. The combined diet of C. calcitrans, T. chuii and I. galbana (C:T:I) could improve the growth and larvae competency of H. arguinensis.

Optimizing Growth and Rearing Techniques for Larvae and Juveniles of the Sea Cucumber Holothuria arguinensis

“…It was only after the settlement stage (between the 16th and 21st days of the trial) that differences in survival were registered, as Holothuroids fed RbCc presented a significantly higher survival (28.83 ± 8.35%) than either RbPt (11.19 ± 3.59%) and RbSm (7.70 ± 6.76%). Looking at the overall survival percentages, between the 3rd and 21st days of trial (RbPt = 4.98 ± 3.41%; RbSm = 4.35 ± 3.82% and RbCc = 10.79 ± 7.84%), only RbCc treatment manages to reach similar survival percentages obtained in previous trials (8.5% with Holothuria leucospilota and 11.66% with Holothuria arguinensis) [11,21]. As all tanks were maintained under the same conditions, with the same settlement substrata, this marked increase in survival suggests an effect of diet RbCc.…”

“…At the start of the trial, there was a significant reduction in the number of observable individuals across diets, as to be expected from the embryonic stage [16,17,21,27,29]. While there were no differences between treatments at this point, this sharp decline in observable individuals is what most likely influenced the low overall survival percentages at the end of the trial.…”

“…Water temperature during larval rearing was higher than at the collection spot to increase embryo and larval survival [21,22], and water quality parameters were measured daily with a multiparametric sonde All tanks were provided with light aeration through diffusing stones so that air bubbles would not damage the developing larvae. Water temperature during larval rearing was higher than at the collection spot to increase embryo and larval survival [21,22], and water quality parameters were measured daily with a multiparametric sonde (YSI-Pro Plus, Yellow Springs, Ohio, USA), followed by water changes of up to 50% to assure stable levels of dissolved oxygen and pH, as well as to maintain nitrogen compounds at untraceable levels, whenever needed. These nitrogen compounds (NH 3 , NH 4 + and NO 2 − in mg•L −1 ) were measured with colour tests (API FishCare, UK), with a detection capacity between 0.25 and 5.00 mg.L −1 .…”

“…Previous studies have already paved the starting point for growth trials with this species, highlighting the nutritional benefits of certain microalgae during the larval stages, such as Chaetoceros calcitrans [21]. Some authors have focused on factors relating to settlement but with other species.…”