Abstract

Captive raised jellyfish frequently suffer from "inversion syndrome," when the bell of a jellyfish permanently flips from concave to convex, exposing the manubria and gastric cavity. This condition results in jellyfish mortality as they are unable to move well and are unfit for aquarium display. Despite its prevalence, this syndrome has not been formally evaluated. The objective of the study was to characterize inversion syndrome through: 1) histopathology of non-inverted and inverted jellyfish (jellies); 2) elemental analysis of non-inverted and inverted jellyfish; 3) aquarium visits involving observations, illness staging, jellyfish measurements, and nutritional analysis of jelly feed; and 4) questionnaires assessing husbandry and environmental conditions correlated with the presence of inversion. The hypotheses of this study were: 1) inversion syndrome is caused by a weakness in swimming musculature preventing the bell from pulsing and maintaining its normal conformation; 2) there is an important element present in non-inverted jellies but deficient in inverted jellies; and 3) there is either a nutritional deficiency or a husbandry concern at aquariums with a high prevalence of inversions. Histopathology results indicate both muscle breakdown and extracellular matrix (mesoglea) degeneration in inverted compared to non-inverted jellies. While only significant for zinc in Aurelia aurita, elemental analysis results show elevations in zinc and iron concentrations in inverted specimens and slight decreases in magnesium in inverted compared to non-inverted jellies. Proximate analysis provides ranges of nutritional components for jellyfish feed but does not show an obvious deficiency in any food source between aquariums. Questionnaires indicate there may be more inversions in aquariums with closed water than semi-open or open water systems. Furthermore, there is a range of inversion prevalence between institutions with some only seeing the condition in 1-2% of their jellies and others seeing it in >30% of their jellies. Inversion is most frequently expressed in two stages of the jellyfish lifecycle. Young growing jellies (~1-2 months old) commonly invert, potentially related to a genetic defect causing a weak or undeveloped mesoglea. Older jellies (~1 year old) often invert, likely due to nutrition, environmental change, or a delayed onset genetic defect in the mesoglea. These results indicate that inversion syndrome is a complex phenomenon which may be minimized with improved husbandry and maintenance of genetic diversity within captive jellyfish communities. Husbandry recommendations include routine system bleaching to remove hydroids, discontinuing the use of old polyp colonies, and maintaining a medium (~10-20L/minute) flow rate. In addition, future studies will continue to improve jellyfish welfare and aid in developing a better understanding of this condition.

Acknowledgements

The authors thank the many contributors to this study and the Geraldine R. Dodge Foundation and the Dr. Robert J. Koller Aquatic Medicine Endowment for funding this research.