Aquaculture is central in meeting expanding global demands for shrimp consumption. Consequently, increasing feed use is mainly responsible for the overall environmental impact of aquaculture production. Significant amounts of fishmeal are included in shrimp diets, causing dependency on finite marine resources. Driven by economic incentives, terrestrial plant ingredients are widely viewed as sustainable alternatives. Incremental fishmeal substitution by plant ingredients in shrimp feed was modeled and effects on marine and terrestrial resources such as fish, land, freshwater, nitrogen, and phosphorus were assessed. We find that complete substitution of 20-30% fishmeal totals could lead to increasing demand for freshwater (up to 63%), land (up to 81%), and phosphorus (up to 83%), while other substitution rates lead to proportionally lower impacts. These findings suggest additional pressures on essential agricultural resources with associated socio-economic and environmental effects as a trade-off to pressures on finite marine resources. Even though the production of shrimp feed (or aquafeed in general) utilizes only a small percentage of the global crop production, the findings indicate that the sustainability of substituting fishmeal by plant ingredients should not be taken for granted, especially since aquaculture has been one of the fastest growing food sectors. Therefore, the importance of utilizing by-products and novel ingredients such as microbial biomass, algae, and insect meals in mitigating the use of marine and terrestrial resources is discussed.

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In order to develop a microsatellite typing system for Lepeophtheirus salmonis (Krøyer), a DNA preparation method for individual sea lice suitable for analysis by polymerase chain reaction (PCR) was designed, and the DNA sequences of 50 L. salmonis microsatellite elements were determined. The microsatellites were composed of 60% perfect, 25% imperfect, and 15% compound repeats. Based on the flanking DNA sequences, four microsatellite‐PCR assays were optimized and used in a pilot study to analyse L. salmonis samples collected in Ireland, Norway and Scotland. Two of the microsatellite‐PCR assays targeted polymorphic loci amplifying seven and 10 alleles respectively. The results showed that microsatellite‐PCR typing could detect genetic variation both within and between the L. salmonis groups, and also was capable of amplifying group‐specific alleles.