A captive breeding population of 16 milk conch (Macrostrombus costatus) was established at Florida Atlantic University in February 2024. Milk conch are similar to the important fishery species, queen conch (Aliger gigas). The overarching goal of the project is to develop techniques to reliably produce captive laid egg masses and then transfer this technology to queen conch to assist with restoration efforts. The project has successfully demonstrated that milk conch will lay egg masses in captivity when they are fed primarily from diatom-rich algal turf scrubbers and maintained on a sand substrate with flow through seawater.
The objective of this part of the project was to develop a method to determine the number of eggs in captive laid milk conch egg masses. Counting eggs individually would be highly impractical, as a single egg mass can contain upwards of 250,000 eggs, highlighting the need to efficiently estimate egg quantity. To facilitate this, for one month (June 15 to July 16, 2024), egg masses collected during this period the following values were measured: egg mass displacement, eggs per mm, and egg strand and egg capsule diameters. In addition to these measurements, 10 egg masses were uncoiled to measure total strand length and percent fertilization in the egg mass. Use of a high-resolution microscopy provided accuracy of these measurements along with observations of early embryonic development (Fig. 1), recorded at a level of precision not previously achieved.
From the 37 egg masses that were collected during the one-month observations, the average eggs per mm was 12.8, average egg strand diameter was 801.5 microns, and average egg capsule diameter was 238.2 microns. The percent fertilization for the 10 egg masses that were uncoiled was 98.6%, and the total egg strand length for the 10 masses ranged from 438 – 2005 cm long, which is equivalent to 60,500 – 279,500 eggs, respectively.
Based on this technique it is now possible to calculate the number of eggs per ml from egg mass displacement, which will allow for rapid determination of the number of eggs per egg mass (average of 7,125 eggs per ml of displacement). This will assist with understanding the productivity of a captive breeding population of conch and assist with hatchery rearing. In the future, these methodologies can be transferred to the queen conch to assist with conservation and restoration of the species throughout the Caribbean.