Bull. Eur. Ass. Fish Pathol., 31(2) 2011, 58 Seasonal occurrence of Caligus spinosus and Parabrachiella seriolae (Copepoda) parasitic on cage-cultured yellowtail (Seriola quinqueradiata) at a fish farm in western Japan E. R. Cruz-Lacierda1*, A. Yamamoto1 and K. Nagasawa2 1 Faculty of Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890-0056, Japan; 2 Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima 739-8528, Japan Abstract The occurrence of Caligus spinosus Yamaguti, 1939 (Caligidae) and Parabrachiella seriolae (Yamaguti and Yamasu, 1960) (Lernaeopodidae) parasitic on yellowtail, Seriola quinqueradiata Temminck and Schlegel, 1845, cultured at a fish farm in Nagashima, Kagoshima Prefecture, Japan, was exam- ined. Both parasites were absent on wild-caught juvenile yellowtail (“mojako”) (length=6.5-13cm; weight=5.4-16g) at the time of stocking in net cages. Prevalence and median intensity of C. spinosus infection on the gill rakers were strongly and positively correlated with seawater temperature. Most of the C. spinosus population was adult females (45-100%). Prevalence of P. seriolae found aached at the base of the pectoral fin showed a high and positive correlation with seawater temperature. Most of the P. seriolae population comprised of adult females (78%). No gross pathological changes or host mortality were associated with the presence of either C. spinosus or P. seriolae. Introduction The yellowtail or Japanese amberjack (Seriola and lernaeopodids (Ogawa and Yokoyama, quinqueradiata), greater amberjack (S. dumerili), 1998). Caligids, known as sea lice, are aached and goldstriped amberjack (S. lalandi) are cul- to the skin and gills of host fish and can cause tured in Japan with the yellowtail as the most skin lesions, fish mortality, and production valuable species. Aquaculture of yellowtail in losses in several farmed fish species (Pike and Japan is based on wild-caught juveniles (<15 Wadsworth, 1999). Caligus spinosus Yamaguti, mm long), called “mojako” (FAO, 2005-2010). 1939 is parasitic on the gill rakers of both wild The grow-out phase is conducted in floating and cultured S. quinqueradiata (Ho et al., 2001). net cages and “mojako” stocked in April-May Large-scale mortality due to C. spinosus infec- reach 1.0-1.5 kg by December and 2-3 kg aVer tion has been recorded by Fujita et al. (1968). a one year culture period. The lernaeopodid copepod Parabrachiella seri- olae (Yamaguti and Yamasu, 1960) originally One problem identified in yellowtail culture is described as Brachiella seriolae Yamaguti and infection by parasitic copepods such as caligids Yamasu, 1960, is aached at the base of pectoral * Corresponding author’s email: erlinda@fish.kagoshima-u.ac.jp, [email protected] Bull. Eur. Ass. Fish Pathol., 31(2) 2011, 59 fins, oral cavity and buccal folds of Seriola spp. oral and opercular cavities were immediately (Ono, 1984; Sheppard, 2004; Johnson et al., 2004; examined for parasites. The gills were excised, Hutson et al., 2007). There has never been any and either examined immediately in seawater report of P. seriolae causing disease in farmed or under a dissection microscope, or placed in wild fish in Japan or elsewhere (Johnson et al., labeled containers and frozen at -20°C until 2004). As studies on these parasites are limited, thawing before examination. The parasites were the occurrence of two copepods parasitic on counted and fixed in 70% ethanol. Terminolo- yellowtail cultured at a fish farm in western gies describing the infection follow Bush et al. Japan was conducted to determine whether (1997). Infection intensities were highly skewed the infection is seasonal. shown by large standard deviation (SD) in some points, thus median intensity was included as Materials and methods a measure of central tendency. Scheffe post hoc Collection of yellowtail and examination for multiple comparison test was used to determine copepods differences between the monthly temperature Yellowtail samples were collected from measurements while Pearson coefficient test a single fish stock and a single net cage was done to determine correlation between (32°13’57.85”N and 130°10’52.31”E) belong- infection and water temperature and between ing to Azuma-Cho Fishery Cooperative (ACFC) size of fish and intensity of infection using SPSS in Nagashima Island, Kagoshima Prefecture, version 15. Japan. The island is a dense farming area with about 300 yellowtail cages along an area of The above study was repeated in the next 116 km2 with an average annual production farming season at the same yellowtail farm in of 12,000 tons. Two examination periods were Nagashima, Kagoshima, particularly to examine done, from June 2006 to May 2007 and from caligids on the body surface at the time of stock- May to October 2007. ing of “mojako” on May 15, 2007, and approxi- mately every month thereaVer until August 21, In June 15, 2006, following the stocking of 2007. The same examination protocol as de- “mojako”, 10 fish were collected once a month scribed above was followed with 50 fish samples and at approximately monthly intervals (Table per collection period. The examination was 1) until May 15, 2007. Sample size was limited continued for two more months, until October to 10 fish because of the high value of yellowtail 30, 2007, but the sample size was reduced to 10 and the destructive nature of examination. Fish fish per sampling, with the aim of collecting were collected randomly by hand net, separately additional infection data for P. seriolae. placed in a plastic bag and transported on ice to the laboratory of the Faculty of Fisheries, Daily records of seawater temperature were Kagoshima University. Larger fish (>200 g) were supplied by the ACFC, measured by wireless immediately spiked through the head before system every hour for 24 hours at 1.0 meter placing them separately in plastic bags. The depth on the cage site. The daily 24-hour read- total length (TL) and body weight (BW) of the ings were pooled to calculate the monthly mean fish were recorded and the body surface, nasal, water temperature. Bull. Eur. Ass. Fish Pathol., 31(2) 2011, 60 Identification of Copepods 30% and 10% in February and March 2007. By Caligus spinosus were categorized as chalimus, the end of observation period in May 2007, pre-adult (males and females combined), adult prevalence had started to increase again. female with or without egg sacs, and adult male based on Izawa (1969). Parabrachiella seriolae Although the overall intensity of C. spinosus on were identified as immature females, and adult the gill rakers of yellowtail was low with large females with or without egg sacs, and with or SDs indicating an aggregated distribution, the without an adult male following Yamaguti and highest median intensity at 7.3 in August 2006 Yamasu (1960) and Ho and Do (1984). was strongly and positively correlated with water temperature (r=0.717, p=0.009). There Results was no correlation between mean and median Seawater temperature intensity of C. spinosus on the body surface, and During the June 2006 to May 2007 period, the mean intensity on the gill rakers of yellowtail seawater temperature was significantly highest and water temperature. in August and September, 2006 at 26.5°C (± 0.8) and 26.1 (± 0.4), and significantly lowest in Feb- In the May-August 2007 period, no caligids were ruary 2007 at 14.6°C (± 0.2) (Table 1). In May to detected when yellowtails were newly stocked. October 2007 period, the water temperature was A similar seasonal paern was observed in the significantly highest in August and September, monthly prevalence of C. spinosus on the gill 2007 at 26.2°C (± 1.1) and 27.6°C (± 0.3). rakers of yellowtail at 100% in August with high and positive correlation with temperature Seasonal occurrence and maturation of C. (r=0.950; p=0.05) but not in the mean and median spinosus intensity of infection. Contrary to the previous Table 1 shows that no caligid was detected in observation, C. spinosus was not detected on the June 2006, when the fish were newly stocked body surface of yellowtail. into the fish cage. Prevalence of C. spinosus on the body surface of yellowtail increased to 60% Life stages of C. spinosus found on the body one month aVer stocking in July 2006, then surface consisted of pre-adult males and females, declined to 10% in August 2006, and was not and mating pairs (an adult male guarding a pre- observed thereaVer, except in April 2007 at 10%. adult female). Individuals of C. spinosus found Pearson correlation showed that prevalence of on the gills were chalimus, pre-adults, adult C. spinosus on the body surface of yellowtail was females with or without egg sacs, and adult not significantly correlated with water tempera- males. The majority of the C. spinosus during ture. On the other hand, a distinctive seasonal the entire study period were adult females (45.2- paern in the prevalence of C. spinosus on the 100%), either with or without egg sacs, which gill rakers was seen, indicating a strong and were always found aached to the gill rakers positive correlation with water temperature of the first gill. Chalimus larvae aached to (r=0.734; p=0.007). Prevalence increased to 70% the gill filaments comprised <10% of the total one month aVer stocking, peaking at 100% in C. spinosus population and were detected in August, then started to taper off declining to September 2006 only and in July and August Table 1. Monthly occurrence of Caligus spinosus and Parabrachiella seriolae on yellowtail (Seriola quinqueradiata) in June 2006 to