Lernea cyprinecea

Welicky, Rachel L., Swardt, Jurgen De, Gerber, Ruan, Netherlands, Edward C. & Smit, Nico J., 2017, Drought-associated absence of alien invasive anchorworm, Lernaea cyprinacea (Copepoda: Lernaeidae), is related to changes in fish health, International Journal for Parasitology: Parasites and Wildlife 6 (3), pp. 430-438 : 433

3.1. Molecular identi fi cation of Lernea cyprinecea

The BLAST results from the 18S rDNA sequence fragment (932 nt) obtained in the current study revealed a 99 ‾ 100% identity to all the available 18S rDNA sequences of L. cyprinacea [Genbank: DQ107554 - DQ107557; KM281816; KP235363; KX258625] from the GenBank database. Additionally, the genetic comparisons (uncorrected p-distance and base pair differences) based on a 618 nt alignment length confirmed that the Lernaea species from the current study was L. cyprinacea [GenBank:] ( Table 2).

3.2. Fish condition, organosomatic indices and health assessment index scores

In September 2013, 13 O. mossambicus (178.095 mm ± 40.626 s.d.; 103.327 g ± 85.404 s.d.) were collected from water with a conductivity of 2.15 mS/cm. In August 2016, 16 O. mossambicus (148.563 mm ± 19.054 s.d.; 41.490 g ± 18.480 s.d.) were collected from water with a conductivity of> 13 mS/cm. Before drought, all fish were infected with anchorworms, and the average anchorworm intensity was 22 anchorworms ± 10 s.d. ( Fig. 2 ). During drought, none of the fish collected were infected ( Fig. 2 ). With the exception of GCF, uninfected fish collected during drought were in better health than infected fish collected before drought. On average, compared to fish collected during drought, fish collected before drought had a 0.033 greater GCF value and an HSI value that was approximately 50% less. The SSI values of all fish were similar. The average GSI value for fish collected prior to drought was 6% that of fish collected during drought ( Fig. 3 ). The average HAI scores for fish collected before and during drought were 110.476 ± 10.235 s.d. and 34.375 ± 5.123 s.d., respectively. The mode score for fish collected pre-drought was 3.67 times greater than that of fish collected during drought ( Table 3), indicating that fish collected pre-drought were considered in poorer health relative to those collected during drought.

3.3. Relationships among drought period and condition, organosomatic indices, and health assessment index scores

Drought (which was tied to the presence/absence of anchorworms) was a significant predictor of GCF, HSI, SSI, GSI, and HAI ( Table 4). Prior to drought when anchorworm-infected fish were collected, anchorworm intensity was only a significant predictor for HSI and GSI, and trended towards significant for the HAI ( Table 4). HSI and GSI values decreased with increasing anchorworm intensity, but the strength of these relationships were weak (HSI, r 2 = 0.294; GSI, r 2 = 0.397).

Figures

Fig. 2. A) Lernaea cyprinacea infecting Oreochromis mossambicus. B) O. mossambicus skin damage from L. cyprinacea infection, before drought. C) Uninfected O. mossambicus, during drought.

Fig. 3. Mean ± 1 s.d. condition factor, somatic indices, and health assessment index values from raw data for Lernaea cyprinacea infected and uninfected Oreochromis mossambicus. All infected fish were collected prior to drought in 2013 and indicated in dark gray. All uninfected fish were collected during drought in 2016 and indicated in light gray. GCF = gutted condition factor, HSI = hepatosomatic index, SSI = spleenosomatic index, and GSI = gonadosomatic index. The mean value of each variable is reported above the corresponding bar.