Introduction
Codfarming in Norway is revitalized due to sharp declines in wild quotas and successful development of a selective breeding for Atlantic cod. Rearing of Atlantic cod (Gadus morhua) larvae relies heavily on the availability of suitable live feed that meets larval nutritional requirements while supporting efficient feeding behavior and survival. Rotifers (Brachionus spp.) and artemia (Artemia salina) are currently the standard first-feeding organism in cod larviculture, yet their small size, swimming behavior, and nutritional profile may limit larval growth and robustness during early developmental stages. Nauplii of the barnacle Balanus spp. represent a potential alternative or supplementary live feed, offering larger prey size, distinct motility patterns, and a naturally marine lipid composition that may better match the feeding ecology of cod larvae. This study evaluates the performance of Balanus nauplii and blue mussel eggs (Mytilus edulis) compared to rotifers and artemia as live feed, with particular emphasis on growth, survival during and deformities.
Materials and methods
Eggs and sperm were stripped from sixth-generation broodstock originating from the Norwegian National Cod Breeding Program and fertilized according to the program's standard protocol. Five full-sib families were produced, and fertilized eggs from each family were incubated separately in 25 L conical silo incubators supplied with flow-through ambient seawater at 4–5 °C. Quadruplicat tank design was used and the startfeeding tanks had 190 l volume. 15000 larvae pr tank were used. Water temperature was then gradually increased from 4–5 °C to 10 °C over a period of 5–10 days (approximately 1 °C per day).
Three different startfeeding protocols were compared. Control 1 was the standard protocol at the National breeding program with rotifers and artemia and late weaning. Treatment 2 (T2) protocol 2 used a combination of rotifers and small Balanus nauplia (cryo S) and large Balanus(cryo-L) nauplia that replaced artemia and then weaning. Treatment 3 (T3) protocol used blue mussel (cryo Micro) eggs that replaced rotifers and large and small Balanus nauplia (Cryo S and Cryo L).
Deformities was measured with x-ray at 180 days post hatch.
Results
Protocol 2 gave higher growth rates, condition factor and myotome hights than protocol 1 and 3. Protocol 1 and 2 had the highest survival at 72 dph. Protocol 1 and 2 had lower vertrebral deformities than protocol 3 .
Growth. Standard Length (mm) and Myotome height for control ,T2 and T3 related to days post hatch (dph).
There were no significant differences between treatments in neck deformities. The control group had control group had lower rate of vertebra deformities than the other treatments. The control group also had lower rates of palantine bone deformities. Other deformities such as vertebrae fusion, lordosis, upper jaw/scull and lower jaw had minor differences between treatments, but severity differed. /> />
Discussion
Balanus nauplia as live feed shows potential to replace traditional live feeds at least partly. These live feeds are also relatively early in their industrial development and improvements in products and protocols are most likely to happen. Balanus nauplia production is also interesting as live feed when it comes to securing local value chains in a rapidly changing world. The logistics of the product also raises possibilities for low carbon footprints related to transport. Further development of this new live feed in terms of quality, optimum protocols, carbon footprints, and local value chain security will be important in further research.
References
Puvanendran, V., et al. (2022). Development of cod farming in Norway: Past and current biological and market status and future prospects and directions. Reviews in Aquaculture, 14(1), 308-342.