Novel Husbandry Practices Result in Rapid Rates of Growth and Sexual Maturation Without Impacting Adult Behavior in the Blind Mexican Cavefish

Abstract

Animal model systems are dependent on the standardization of husbandry protocols that maximize growth and reduce generation time. The Mexican tetra, Astyanax mexicanus, exists as eyed surface and blind cave dwelling populations. The opportunity for comparative approaches between independently evolved populations has led to the rapid growth of A. mexicanus as a model for evolution and biomedical research. However, a slow and inconsistent growth rate remains a major limitation to the expanded application of A. mexicanus. Fortunately, this temporal limitation can be addressed through husbandry changes that accelerate growth rates while maintaining optimal health outcomes. Here, we describe a husbandry protocol that produces rapid growth rates through changes in diet, feeding frequency, growth sorting and progressive changes in tank size. This protocol produced robust growth rates and decreased the age of sexual maturity in comparison to our previous protocol. To determine whether changes in feeding impacted behavior, we tested fish in exploration and schooling assays. We found no difference in behavior between the two groups, suggesting that increased feeding and rapid growth will not impact the natural variation in behavioral traits. Taken together, this standardized husbandry protocol will accelerate the development of A. mexicanus as a genetic model.

Keywords: Astyanax mexicanus; behavioral neuroscience; cavefish; evolution; husbandry.

FIG. 1.

Food type and feeding schedule for our novel high growth rate protocol. (a) Twenty-four hours hatched artemia nauplius. (b) Gemma pellet feed. (c) Blood worm tips. (d) Zeigler pellets. (e) Full blood worm. Arrow denotes fish size in SL (mm; distance from nose to caudal peduncle). SL, standard length.

FIG. 2.

SL measurements of surface fish and Pachón cavefish through 5 months of development. SL measurements in millimeters (y-axis) were recoded every 2 weeks (x-axis) until fish reached 50 mm in SL. x-axis starts at week 2 when fish were measured and put onto the recirculating system in the fish facility. Error bars denote ±standard error. Sample size, n = 24 for both surface fish and cavefish. Unpaired t-test with significance values; ****p < 0.0001.

FIG. 3.

Novel tank assay comparing adult Astyanax populations raised with previous and high growth rate husbandry protocol. (a) Tracking traces (grey) from individual novel tank trials, with gray shading representing water column. (b) Cumulative duration of time spent in the top and bottom half of the tank. Previous husbandry protocol (p.p.) and new husbandry protocol (n.p.). Violin plots display minimum to maximum values, with three lines representing the 75th quartile, median, and 25th quartile. Sample size (n = 10) were the same for all populations. ****p < 0.0001.

FIG. 4.

Schooling assay comparing fish from adult Astyanax populations raised with previous and high growth rate husbandry protocol. (a) Swimming tracks representing a single trial of two fish from the same population (e.g., grey = fish 1, black = fish 2). (b) Violin plots of interindividual distance, the average distance in cm between both fish in each trial, normalized to arena diameter (111 cm). (c) Violin plots of centroid speed, average speed calculated from tracking a centroid placed at the middle of each fish. Previous husbandry protocol (p.p.) and new husbandry protocol (n.p.). Violin plots display minimum to maximum values, with three lines representing the 75th quartile, median, and 25th quartile. Sample sizes for surface fish, previous n = 4 groups, and new husbandry protocol n = 5 groups. Sample sizes for cavefish fish, previous n = 8 groups, and new husbandry n = 7 groups. No comparisons were statistically significant.