Outdoor rearing facilities of free spawning calanoid copepods for turbot larva can host a bank of resting eggs in the sediment

Abstract

It is well established in Denmark to rear calanoid copepods in outdoor tanks for use as live feed during turbot (Scophthalmus maximus) larval production. However, the copepod assemblages, composed of a mixture of all development stages and therefore body sizes, vary over time and do not always match the larval needs. When turbot larvae reach metamorphosis and are transferred indoor for weaning, the outdoor tank sediments may reveal vast amounts of copepod eggs undergoing dormancy. Here, we report a copepod species succession firstly among Centropages hamatus and then Acartia spp. both with resting eggs as part of their life cycles as a result of two different nutrients treatments and a control. We found a tendency to a higher egg production and indeed more eggs in the sediment of nutrient amended tanks. In fact close to 5 million eggs per square meter, making up to 400 million eggs per tank was found in the sediment after one production.Instead of discarding the sediment between production batches, we propose to collect it and generate an egg bank. These eggs can be stored for months to a year, however, according to the results, a large loss rate occurred, which could be potentially decreased by the optimization of storage conditions. Those procedures will enable hatchery managers to apply newly hatched copepod nauplii exactly when the turbot larvae start feeding which would potentially solve the, often occurring, mismatch between the time of start-feeding turbot larvae and actual available prey field.

A production season of turbot larvaeScophthalmus maximus(Linnaeus, 1758) reared on copepods in a Danish (56°N) semi-intensive outdoor system

“…At the end of a production in a tank, the copepod eggs can also be harvested and cold stored and be used to boost first feeding tanks with nauplii by hatching the collected and stored eggs into nauplii (Hansen et al . ). Further, the stored eggs could be hatched and used in a combination food scheme when the larvae are weaned to formulated feed in the indoor system.…”

“…This practice enables the adult copepods more time to reproduce, securing higher amounts of nauplii stages I‐III ensuring a better chance for obtaining enough nauplii as prey item for the first‐feeding turbot larvae. Alternatively or additionally, copepod eggs from established egg banks of quiescent eggs extracted from sediment material from earlier production cycles could be hatched and the nauplii introduced as first feed (Hansen, Blanda, Drillet, Højgaard, Mahjoub & Rayner ).…”

Review: A bibliometric survey of live feed for marine finfish and shrimp larval production

“…In the western world, we know of decade's long large scale outdoor copepod production systems in Norway (e.g. van der Meeren et al, 2014) and Denmark (Engell‐Sørensen et al, 2004; Blanda et al, 2016; Hansen et al, 2016; Jepsen et al, 2017). Intensive indoor copepod rearing systems are implemented in, for example, USA (Sarkisian et al, 2019) and most likely both extensive and intensive copepod production systems exists several other places we do not know about.…”

Timing of embryonic quiescence determines viability of embryos from the calanoid copepod, Acartia tonsa (Dana)

“…overwintering [ 46 ]. Moreover, it is an aspect of relevance for optimizing protocols for generating culture egg banks in relation to live feed products for marine fish hatcheries [ 44 , 47 ]. The findings of the present study open new opportunities for cold-storing copepod eggs.…”