Use of non-ablated shrimp (Litopenaeus vannamei) in commercial scale hatcheries

Abstract

The Pacific white shrimp (Litopenaeus vannamei), is currently the most cultured marine shrimp worldwide with 78% of global shrimp production in 2019 and it represents an important marine food source for consumers. Induction of rapid egg production in captivity of this shrimp is usually induced by unilateral eyestalk ablation which involves the removal or constriction of one eyestalk through cutting, cauterizing or tying to reduce the level of hormone that inhibit reproduction of shrimp in captivity. However, due to physiological imbalance and stress caused by this practice, it has attracted attention as an animal welfare issue. As a result the need of using eyestalk intact animals in hatcheries has become a priority for producers, retailers and seafood certifiers. The main goal of this thesis was to provide a body of evidence on potential of using non-ablated female in commercial shrimp hatcheries to support on-going dialogue around the continued use of unilateral eyestalk ablation in modern L. vannamei breeding practices. First the feasibility of using shrimp non-ablated female (NAF) in modern egg production practices was evaluated and the quality of their offspring was assessed from early development stage to marketable size shrimp. NAF produced significantly more eggs and nauplii than ablated female (AF) (p < 0.05). However their level of productivity (eggs and nauplii per tank/day) was significantly lower than AF (p < 0.05). In addition, their offspring had similar growth and final survival to those from AF from early development stage to marketable size shrimp (p > 0.05). However, salinity stress tests indicated that postlarvae from NAF have significantly better resilience (p < 0.05). The second study assessed the effect of fresh-frozen natural feed (squid and polychaete) at pre-maturation stage on NAF productivity, their biochemical composition and offspring quality. Fresh-frozen natural feed did not improve NAF productivity as it was significantly lower to AF (p < 0.05). In addition, this practice did not affect their offspring quality (biochemical content, growth performance and survival) (p > 0.05). However, their fertilization rate increased and the hepatopancreas had significantly higher levels of total lipid, total saturated and monounsaturated fatty acids, linoleic acid (LA), arachidonic acid (ARA) and eicosapentaenoic acid (EPA) when compared to other females (p < 0.05). After this, based on higher survival observed on postlarvae from NAF after salinity stress tests (SST), it was proposed to verify if the possible resilience of postlarvae produced from NAF broodstock would be expressed following a disease challenge, including at juvenile stage. There was a significant higher survival of postlarvae from NAF when challenged with Vibrio parahaemolyticus (p < 0.05). No significant difference was observed between the juveniles from NAF and AF when challenged with white spot syndrome virus (WSSV) (p > 0.05). At last, there was evaluated the impact of shifting from AF to NAF L. vannamei based maturation facilities system on production costs and profitability. This change increased nauplii production cost however this may not be reflected at larviculture level. The profitability modeling showed that if the farmers switch to source animals produced on NAF maturation facilities based system, they would reduce the level of financial losses caused by acute hepatopancreatic necrosis disease (AHPND) and WSSV. In summary, this thesis provides a new scientific knowledge and relevant evidence to support the phase out of unilateral eyestalk ablation in shrimp hatcheries and working toward improvement of NAF productivity.