Maternal Stress Effects on Hatching Success and Larval Malformation Prevalence in Palmetto Bass.

Abstract

Striped Bass Morone saxatilis are an iconic North American fish. This species, and it’s hybrid with White Bass Morone chrysops, Palmetto Bass are intensively cultured for stocking into Texas water bodies. However, a large proportion of hatchery‐spawned Palmetto Bass larvae were recently plagued with malformations. Pug headedness is a common malformation that restricts the fish’s ability to intake food by misshaping the skull and mouth. Malformations such as this drastically reduce larval survival. Female Striped Bass broodfish used to produce Palmetto Bass are caught in the wild, hormonally induced to maturation, transported to the hatchery, and hand‐spawned by stripping. Consequently, we hypothesize that this extreme handling stress affects larval development and viability. Eight Striped Bass females were strip‐spawned, and samples of plasma, ovary, eggs, and hatchlings where collected to measure the concentrations of glucose, lactate and cortisol. Percentage of hatch, malformations and viability were also recorded for each spawn. A standard ELISA plate was used to measure cortisol and colorimetric protocols were used to measure glucose and lactate. Females that produced spawns with lower hatch (9.9 %) and larvae with elevated malformations rates (53.2%) showed significantly higher concentrations of plasma cortisol (290.7 ± 80.7 ng/mL) than females associated with low larval malformation rates (120.6 ± 16.0 ng/mL). Interestingly, females with low hatching rate had significantly less cortisol in ovarian tissue but more cortisol in their eggs than females with a higher performance. Spawns with higher malformation rates also had higher values of larval tissue cortisol (4.5 ± 1.0 ng/g) than spawns with lower malformation rates (0.2 ± 0.0 ng/g). This data points to a transfer of cortisol from maternal gonads to the spawn while under handling stress. Glucose and lactate had similar values in all individuals. Thus, only cortisol correlated with the presence of malformations in larvae. This study demonstrates the need to reduce handling stress in Striped Bass culture to minimize the production of malformed larvae. The impact of integrating saltwater baths, anesthetics, and reducing handling time, can be easily monitored with cortisol measurements and may improve production outcomes.