Stephanie Grodeska | 11/2/2016 9:00:21 PM
Utilization of above ground pools at low salinities is practical for production of a large number of cocahoe minnow eggs. Production of eggs is achievable outdoors throughout the summer, with peaks in spring and fall (April or early May and September and October). Using pools to spawn cocahoe minnows is practical for multiple reasons. Most predators, such as birds, can be excluded by using netting to cover the pool. Little water exchange is involved when using pools containing dirt, which helps to regulate nitrogenous waste. Pools typically contain lower numbers of broodfish, and river silt or other organic bottom cover can be used as both filter and waste trap. It is also easier to observe fish in small pools than fish in ponds.
Research Study: For the experiment at the AgCenter Aquaculture
Research Station, 500-gallon pools were used. Two weeks prior to
stocking, all pools were filled and fertilized daily with approximately
1.5 ounces of powdered feed (45 percent protein). Approximately
25 pounds of salt was added to each pool, which resulted in 5 ppt
salinity. A regenerative blower supplied continuous aeration to all
pools via air stones. The pools were stocked at a 2:1 female: male
ratio. A synthetic spawning substrate or mat (Spawntex®) was used
for the females to deposit eggs. Eggs were harvested from the mats every 3-4 days from April to October. Water
was added as needed to maintain depth in the pools.
Stocking and Feeding: For experimental purposes, groups of pools were stocked with different numbers of
females, but we found that a ratio of 60 females: 30 males resulted in the most eggs. Fish were fed a commercially
available 45 percent protein, 12 percent fat, 2.4 mm diameter, extruded feed once daily at 3.5 percent of initial
body weight per day. This percentage was constant throughout the study and adjusted for growth at two and three
months after initial stocking. Currently studies indicate that a 40 percent protein, 9 percent fat ration could be
cheaper and have similar results.
Water Quality: Prior to stocking and weekly thereafter, dissolved oxygen (DO), pH, salinity, total ammonia
nitrogen (TAN), total alkalinity, and total hardness were recorded for each pool. Salinity was maintained at 5-6 ppt
using rock salt. Temperature ranged from 67 °F to 88 °F. Water quality
parameters were maintained within acceptable ranges: DO remained
above 5.5 mg/L, pH ranged from 8.2 to 9.2, salinity ranged from 4.7 to
9.5 ppt, TAN ranged from 0 to 1.4 mg/L, alkalinity ranged from 310 to
900 mg/L, and hardness ranged from 200
to 420 mg/L. In June, temperature was reduced by placing Styrofoam
panels over each pool for shade.
Egg Collection: A Spawntex® spawning mat was placed in each pool
for spawning substrate. These mats are constructed of coconut fibers
with a latex binder on a polyester net backing. Spawning mats were cut
into 18 x 24 inch sections, placed on a wire frame, and then suspended
6 inches below the water surface from two floats made of sealed PVC tubing. Spawning began within 24 hours after mats were placed in
pools. The mats were collected twice per week and replaced with clean
mats. Depending on preference, egg-laden mats can be transferred into a
hatching pool/pond for water incubation, or the eggs can be removed for
For the purpose of the experiment, we needed to remove eggs from the
spawning mats in order to quantify the numbers produced from each pool.
Eggs were removed by manually tapping and shaking mats against a rigid
screen positioned over a water-filled, plastic container. Egg-laden water
from the container was poured through
nylon mesh (window screen) to collect the
eggs. The eggs were separated from debris
(algae, mat fibers, etc.) in order to quantify the numbers volumetrically. We found
that 1 mL of eggs is roughly equal to about 100-120 eggs, as these eggs tended to
decrease in size across the spawning season. Not all eggs produced are fertilized and/
or viable, but the live eggs (brown pigment) can easily be distinguished from the dead
eggs (white in color) as seen in Figure 4. After collection the eggs can be placed in
hatching jars or be air incubated (see Air Incubation Fact Sheet).
Egg Production: Throughout the study period, the 360 females stocked out produced more than 380,000 eggs.
Egg production varied monthly due to natural semi lunar (tidal) cycles, with peaks occurring between full and
new moon phases. The overall peak in egg production occurred between April and mid-May, when weekly water
temperatures ranged from 75 °F to 83 °F (24 °C to 28 °C).