Ultrasound imaging analysis involves development of an effective combination of physical properties, equipment, instrument settings, and protocols. This review focuses on the application of ultrasonography to fish reproduction. The goal was to assemble a comprehensive reference data set to serve as a decision‐enabling tool for potential users. The specific objectives were to (1) identify the ultrasound equipment, settings, and procedures used during examination, (2) review the fish handling procedures used during examination, and (3) review current data on sex identification and reproduction indices developed using ultrasonography. The 27 studies selected for inclusion in this review represent 21 fish species. Most (96%) of the studies reported the model name for the ultrasound unit, but only 19% reported the probe model. The most reported probe features were the frequency capability (96% of the studies) and array format (linear, sector, or annular; 81%). The majority of the studies (89%) did not report any of the control settings used. The combinations of handling and ultrasound procedures were variable even within the same species, and the majority (78%) of the studies included a form of restraint. None of the studies simultaneously integrated the use of unrestrained, unanesthetized, submersed fish with a submersed waterproof probe, which would enable the use of water as a transmission medium for ultrasound. Size, life stage, gonadal growth of reproductively active adults, and fish morphology influenced the ability to use ultrasonography for sex identification and the development and application of qualitative and quantitative reproductive indices. The utility of ultrasonography in fish reproduction has been repeatedly validated, and innovative indices for noninvasive use have been developed. However, this review identifies a clear lack of consistency in reporting of instrument settings and handling procedures and provides suggestions for standardizing the use of ultrasonography with aquatic species.

Gonad development in 4‐year‐old triploid and diploid ornamental koi, a variant of Common Carp Cyprinus carpio, from corresponding heat‐shocked and control progenies was investigated. Diploid males were normally mature. Triploid males from heat‐shocked progeny demonstrated development of testes typical for triploid fish; triploid males did not release sperm and their testes had a pinkish color and were significantly reduced in size. Diploid females were normally mature and their gonadosomatic indices (GSIs) varied from 7.5% to 30.7% and the mean value was 21.3%. Triploid females had unexpectedly well‐developed ovaries, which were filled with fully grown oocytes; their GSIs varied from 4.2% to 30.1% and the the mean value was 17.0%. Four triploid koi females released large quantities (from 260,000 to 394,500 eggs per female) of ovulated eggs after hormonal injection. Eggs from triploid females were fertilized with sperm from normal diploid koi males. Mass mortality of hatched larvae occurred at the swim‐up stage, but about 32,000 swim‐up larvae were obtained and stocked for further rearing. A total of 248 juveniles (or less than 1% from the number of stocked larvae) were collected from outdoor tanks. Ploidy analysis of juveniles (n = 110) showed that most of them were aneuploid with ploidy ranging from 2.3n to 2.9n with a mean value of 2.6n; two juveniles were diploid (2n). This shows that triploid koi females produced aneuploid eggs with a ploidy range from haploid to diploid level with the modal ploidy level around 1.5n, similar to the production of aneuploid spermatozoa observed earlier for triploid males in fish.

The present study was focused on the discovery of single‐nucleotide polymorphisms (SNPs) and measuring genetic variation in three YY‐male and five mixed‐sex Nile Tilapia Oreochromis niloticus strains, which are available in the United States. We performed restriction site‐associated DNA sequencing for SNP discovery and genotyping. Overall, 31,813 SNPs were identified and used to measure both intra‐ and interstrain genetic variation. Mean expected heterozygosity (He) ranged from a low of 0.084 in the Miami YY strain to a high of 0.222 in the Miami mixed‐sex strain. Two of the three YY groups (Miami YY and Fishgen YY Red) had the lowest He values (0.084 and 0.085, respectively) and the second‐ and third‐lowest observed heterozygosity (Ho) values (both Ho = 0.107). The number of private alleles varied from 90 to 3,795 in different strains and tended to increase with increasing He. Inbreeding, as measured by FIS, was found to be low in all populations, ranging from −0.060 ± 0.004 (mean ± SE) in the Fishgen YY Dark strain to 0.04 ± 0.0093 in the GIFT (Genetically Improved Farmed Tilapia) strain; this indicates that the analyzed strains are currently being maintained with approximately random mating of individuals. Genetic differentiation between populations, as measured by pairwise FST, ranged from little differentiation (FST = 0.06 for the Ismailia Canal and GIFT strains) to strong differentiation (FST = 0.32 for the Miami YY and Lake Manzala strains). The discovered SNPs and quantification of genetic variation can be used for parentage determination and high‐throughput pedigree reconstruction as well as for determining the optimal interstrain crosses to achieve heterosis.

This study addressed the development of rapid, straightforward, and minimally stressful procedures for the ultrasound imaging of ovaries of channel catfish Ictalurus punctatus in a commercial hatchery setting. The objectives were to (1) describe the ultrasound imaging equipment and settings used, (2) describe the fish handling procedures during imaging, and (3) illustrate image orientation with respect to the physical positioning of the probe and the catfish. Ultrasound images of the ovaries of channel catfish were recorded as digital video recordings (audio video interleave format) and as still images (ultrasound image format files). This study integrated the use of nonanesthetized, submersed fish within a recirculating tank system or portable container and a submersed waterproof probe, which enabled us to use water as a transmission medium for ultrasound. This allowed us to image the fish in ventral recumbency (upright swimming position) without using a physical restraint in the tank system, or by positioning the fish in the portable container by adjusting the position of its caudal peduncle with one hand and that of the probe with the other hand. The ease of using this technique allows it to be employed as a systematic method for fish handling under laboratory and hatchery conditions. The detailed ultrasound imaging procedures and instrument control settings reported can be used in future testing, improvement, and standardization of procedures for viewing ovaries in channel catfish and potentially other species.

Commercial production of hybrid catfish (female channel catfish Ictalurus punctatus × male blue catfish Ictalurus furcatus) is reliant on interdependent biological, environmental, and technical procedures. This study addresses one of these critical components – the evaluation of channel catfish ovarian development based on sonographic analysis. The objectives were to: (1) develop a channel catfish ovarian ultrasonography index, (2) test the effect of the spawning trials on fertilization estimates of fish assessed using the ultrasonography index, and (3) evaluate the expected (hypothesized) and observed outcome of the ultrasonography assessments. Seven ovarian morphology classifications were developed based on ultrasonography of 915 channel catfish (N = 915 images), and 210 females were selected for spawning. The predictions based on the classifications prior to hormone injection showed a significant effect (P < 0.002) on the observed outcomes (viable or nonviable eggs). The probability of correct classification was 0.86–0.89 for Categories 3 (developing), 4 (advanced), and 5 (mature), and 0.93–1.0 for Categories 1 (undeveloped), 2 (underdeveloped), 6 (spawned), and 7 (atretic). The ultrasonography index covered the full range of ovarian dynamics (i.e., recrudescence through spawning). It provided an unobtrusive, direct method of ovarian assessment to work toward improving the efficiency of broodstock selection.