This study evaluated the performance of lettuce (Lactuca sativa) cultivated in coupled aquaponic systems integrated with Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) under tropical greenhouse conditions. The experiment was conducted across two consecutive lettuce production cycles to assess fish growth, plant performance, water quality, and nutrient dynamics. African catfish exhibited significantly higher specific growth rates (1.08 ± 0.18%/day; p = 0.02) and weight gain (92.38 ± 22.29%; p = 0.03) compared with tilapia. During the first lettuce cycle, tilapia-based systems yielded significantly higher final plant weights (177.6 ± 34.4 g/plant; p = 0.0002), and greater increases in leaf number, weight gain, and absolute growth rate than catfish-based systems. However, in the second cycle, catfish systems resulted in superior lettuce leaf morphology, with significantly greater leaf length, width, and total leaf area. Nutrient profiles differed markedly between systems. In the deep-water culture (DWC) units, total phosphorus (TP) concentrations were significantly higher in the tilapia-based system during cycle 1 (12.39 ± 0.64 mg/L; p = 0.0001), while total nitrogen (TN) concentrations were significantly higher in the catfish treatment during cycle 2 (21.54 ± 2.93 mg/L; p = 0.0007). Catfish-based systems also showed higher levels of calcium and sodium. Despite these differences, temperature, pH, and dissolved oxygen remained within optimal ranges for aquaponic production across both systems. Overall, tilapia-based aquaponics promoted faster early-cycle plant growth and higher initial yield, whereas catfish-based systems enhanced nitrogen availability and improved lettuce leaf structural development over successive cycles. These findings indicate that fish species selection plays a critical role in shaping nutrient dynamics and crop performance in tropical aquaponic systems.

Rice yellow mottle virus disease, caused by Rice yellow mottle virus (RYMV), is the most important disease of lowland rice in Uganda. However, little is known about its genetic diversity in Uganda and relationships with other strains elsewhere across Africa. A new degenerate primer pair that targets amplification of the entire RYMV coat protein gene (circa 738 bp) was designed to aid virus variability analysis using RT-PCR and Sanger sequencing. A total of 112 rice leaf samples from plants with RYMV mottling symptoms were collected during the year 2022 in 35 lowland rice fields within Uganda. The RYMV RT-PCR results were 100% positive, and all 112 PCR products were sequenced. BLASTn analysis revealed that all isolates were closely related (93 to 98%) to those previously studied originating from Kenya, Tanzania, and Madagascar. Despite high purifying selection pressure, diversity analysis on 81 out of 112 RYMV CP sequences revealed a very low diversity index of 3 and 1.0% at the nucleotide and amino acid levels, respectively. Except for glutamine, amino acid profile analysis revealed that all 81 Ugandan isolates shared the primary 19 amino acids based on the RYMV coat protein region examined. Except for one isolate (UG68) from eastern Uganda that clustered alone, phylogeny analysis revealed two major clades. The Ugandan RYMV isolates were phylogenetically related to those from the Democratic Republic of Congo, Madagascar, and Malawi but not to RYMV isolates in West Africa. Thus, the RYMV isolates in this study are related to serotype 4, a strain common in eastern and southern Africa. RYMV serotype 4 originated in Tanzania, where evolutionary forces of mutation have resulted in the emergence and spread of new variants. Furthermore, mutations are evident within the coat protein gene of the Ugandan isolates, which may be attributed to changing RYMV pathosystems as a result of rice production intensification in Uganda. Overall, the diversity of RYMV was limited and most noticeably in eastern Uganda.