|Although hybrid catfish that are produced from channel female (Ictalurus punctatus) and blue male (Ictulurus furcatus) display superior characteristics for aquaculture, hybridization successes in natural environments are low and not completely understood compared to reproduction of channel catfish. Five experimental runs were conducted under hatchery conditions to determine relationships between external appearances, body metrics, and the ratios of body metrics of channel catfish and blue catfish brooders and reproductive successes (spawning rate, 1st spawning time, number of eggs per kg female, % viable eggs, % hatching rate, % swim-up fry, and number of fry per kg female). The study was also designed to identify spawning behaviors occurring at 1, 3, 6, and 12 h prior to spawning and differences in percentages of brooders that exhibited behaviors, frequency/h/fish, and time duration of each behavior between the channel and blue brooders that spawned or did not spawn. Correlations of body metrics, behaviors, and spawning successes were also determined. Information obtained was used to determine criteria of good broodfish for reproduction and give possible explanations for the differences in spawning successes between channel x channel (C X C) and channel x blue (C X B) and (B X B). All female brooders were injected with carp pituitary (10 mg kg-1) while no injections were given to males. External coloration, body metrics and their ratios were measured before randomly stocking them into aquarium system. Camera system was installed to record spawning behaviors during experimental period.
Selection of the channel brooders can be a factor affecting the spawning successes in some cases. The results from this study showed the broodfish that spawned and did not spawn exhibited some differences in terms of body coloration, body metrics and the ratios of body metrics. Channel female spawners had smaller ratios of body length-to-width and length-to-girth than the ratios of the non-spawners. Channel males that spawned had a smaller length-to-head width ratio compared to the channel males that did not spawn. In addition, the differences in body ratios also correlated with differences in spawning successes. Channel females having the ratios of length-to-width less than 5.5 and length-to-girth less than 1.9 spawned more successfully than those with the larger values. The females in this study with the similar sizes (46.5 – 62.9 cm) having the larger measures of body girths (≥ 28 cm) and widths (≥ 9 cm) had higher spawning rates than those with smaller girth and width measures. Likewise, the males spawned better when they had smaller ratios of length-to-head width (≤ 5.5) or dark “underside” coloration of head.
Spawning behaviors between brooders that spawned and those that did not spawn significantly differed. The percentages of channel males that spawned exhibited dancing and curling behaviors statistically higher than those of the non-spawners from 6 to 1h before the first eggs were observed. Additionally, the males that spawned danced and curled females more frequently than the male non-spawners. Similarly, spawning channel females had a greater proportion of the females displaying dancing behavior than the females that did not spawn. The frequencies of rubbing, dancing and air releasing behaviors of the spawners were more than those of the non-spawners.
In this study, the ovulation rate of channel females induced with carp pituitary was similar as they paired with channel males (74.2%) or blue males (70.0%). Hormone-induced blue females paired with blue males (B X B) also resulted in 69.2% of the females releasing eggs. However, the percentage of eggs masses ovulated that fertilized by C X C was significantly higher than that from C X B and B X B. Overall, 91.3% of eggs masses from C X C were fertilized while the values for C X B and B X B were 14.3% and 33.3%, respectively. The viability per egg mass of C X C, C X B, and B X B was not different and ranged from 49.2 to 77.4%. The results suggest that although carp pituitary was effective in inducing females to ovulate in many cases, the males may have not fertilized them and quality of the males may be an issue that caused the differences in fertilization rate. Behavior of male blue and channel catfish were similar; however, for spawners and non-spawners, there were differences in the percentage of males showing a given behavior and frequencies/h between behaviors. Overall, spawning successes of channel catfish can be improved based upon morphological characteristics and low natural hybridization might be issues of blue male catfish.