Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 153 Deformations in reciprocal hybrids of salmon ( salar L., 1758) and (Salmo trutta m. trutta L., 1758) aged 0+ and 1+

L. Kirczuk* and J. Domagała

Department of General Zoology, University of Szczecin, ul. Felczaka 3c, 71-415 Szczecin, Poland

Abstract The study was performed on 416 hybrids ♀ trout x ♂ salmon and 158 hybrids ♀ salmon x ♂ trout aged from 4 to 24 months. The fish was obtained in a series of 8 experiments in which reciprocal hybrids were grown of salmon and trout caught from the natural conditions. The hatch was introduced to the watercourses that had no outlet to open water. After catching the hybrids were weighed, measured, their appearnce was described and they were fixed. In the fixed material the first arch branch and pyloric caeca were analysed. The analysis revealed morphological changes in the shorter arm of the gill arch that was narrower from the remaining part of the arch and some gill rakers were missing. The changes were observed in 52% hybrids of trout x salmon and 12% hybrids of salmon x trout. Changes were also noted in the pyloric caeca, which were untypical, tumorous and unevenly distributed. The deformations were identified in 94% of trout x salmon and 58% salmon x trout hybrids. The changes in the branchiostegal membrane and losses in the bones of the gills cover were observed in 27% trout x salmon and 22 % salmon x trout hybrids. At least one type of deformation was noted in 95.3% of trout x salmon and 70% of salmon x trout hybrids.

Introduction et al., 1998) and restitution of salmon over a Hybridisation between salmon and trout in limited area (Jansson & Öst, 1997). Hybrids natural conditions at the sites of their common of salmon and trout are also increasingly occurrence is rather frequent. It varies from often met in rivers where in the population 0.15% in Finland and (Elo et al., 1995) of salmons a growing contribution of dwarf to 18.8-31.4% in the Baltic Sea basin (Semenova males appears. The number of dwarf males & Slyn’ko, 1988). The reasons stimulating increases with decreasing abundance of hybridisation between these species include the salmon population (Jansson et al., 1991; a reduction of the spawning areas in the Elo et al., 1995) and they show aggressive regions of common occurrence of salmon and reproduction behaviour (Beall et al., 1997; trout caused by growing anthropopressure, Garcia-Vazquez, et al., 2002). Hybridisation (Hammar et al., 1991; Elo et al., 1995; Delling between these species is undesirable as it et al., 2000), excessive catch of fish (Makhrov leads to the loss of spawning sites of pure

* Corresponding author’s Email: [email protected] Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 154 species (Garcia-Vazquez et al., 2003) and can Henceforth, as it is generally accepted, in the be responsible for considerable introgression names of hybrids the maternal species is given (Verspoor, 1988; Garcia de Léaniz & Verspoor, first and paternal second (Chevassus 1979; 1989). This aspect has been previously studied Goudie et al., 1993; Galbreath & Thorgaard, in reciprocal hybrids between salmon and 1994; Blanc, 2003). trout and in other species hybrids (Iuchi et al. 1975; Bakos et al. 1979). Such distortions can All the hybrids caught were subjected to have a large influence on growth and survival analysis of deformations that often appear in of the hybrids (Bakos et. al.1978). Analysis in fish hybrids (Bakos et al. 1979; Beck et al. 1984; the presented study showed, that salmon and Kazakov et al. 1984; McGowan & Davidson trout hybrids have a surprisingly high level 1992; Gray et al. 1993) and influence the of atypical features in external and internal number of rakers on the first gill arch and the morphology. number of pyloric caeca. The deformations were divided into the anomalies of the first gill Material and methods arch, pyloric caeca and the external anomalies In the years 1994-2003 eight experiments were including deformations of the operculum performed in which reciprocal crossing of covering the gill slits, branchiostegal salmon and trout was made during artificial membrane and the partition separating two spawning. The salmon spawn and milt were branchiostegal membranes. obtained from individuals grown in the Fish Farm in Miastko and in the River Wieprza, Results originating from the school imported from the The first arch of the gills River Dougava, while the trout spawn and milt Some of the trout x salmon hybrids were found were taken from the school brought from the to have untypical first gill arch. Morphological River Rega. Fertilisation was performed at the analysis revealed a shorter arm of the first gill PZW Hatchery in Goleniow, where the spawn arch, narrower than the remaining part of the was also incubated. The hatch was introduced gill arch and missing some gill rakers (Figure into the watercourses near Szczecin, ending 1). Along the remaining section of the gill arch in the municipal sewage system, which the gill rakers grew off the sides of the arch, ensures that the hybrids would not get into were accumulated in the arch curvature and the natural environment to have contact with irregularly distributed (Figure 2). The changes pure species. The growing fish were regularly led to a decreased number of the gill rakers caught with the help of electric current on the first gill arch; in the trout x salmon producing aggregate JUP-23 (Approved by hybrids aged 0+ this number was 17.15 (7-22), the Local Commission for Ethical Research while in the hybrids aged 1+ it was 14.82 no. 24/02 of 3.06.2002). The study was made (9-23). Anomalies of the first gill arch were on 416 hybrids of ♀ trout x ♂ salmon and 158 noted in 44% of individuals aged 0+ and hybrids of ♀ salmon x ♂ trout (Table 1) aged 75.3% of individuals aged 1+, so in total 52% from 4 to 24 months. The hybrids grew up of all trout x salmon hybrids. In the reciprocal separately in neighbouring water–courses. , salmon x trout, similar deformations Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 155

Figure 1. The arch of the gills from ♀ trout x ♂ Figure 2. The arch of the gills from ♀ trout x ♂ salmon hybrid aged 15 months, the missing gill salmon hybrid aged 10 months, with gill rakers rakers over the section a (a), scale of 1 mm. missing over the section a (a) and of different lengths (w), scale of 1 mm.

Figure 3. A section from the alimentary track of Figure 4. A section of the alimentary track of a a 7-month old trout x salmon hybrid with pyloric 7-month old trout x salmon hybrid with irregularly caeca (pc) of different lengths, scale of 1mm. distributed pyloric caeca of different lengths, scale of 1mm. Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 156

Figure 5. ♀ Trout x ♂ salmon hybrid aged 21 months, Figure 6. ♀ Trout x ♂ salmon hybrid aged 22 the losses in the opercular and subopercular bones, months, the losses in the opercular, subopercular scale of 1.5 cm. and interopercular bones, scale of 1.5 cm.

Figure 7. ♀ Trout x ♂ salmon hybrid aged 19 Figure 8. ♀ Trout x ♂ salmon hybrid aged 21 months, the losses in all bones of the opercular months, the deformations in the gill cover and bones deshielding the gill arches, scale of 1.5 cm. extended partition, scale of 1 cm. Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 157 of the first gill arch were observed in 12 % bones (Figure 6). The deformed bones exposed of all salmon x trout hybrids (10 and 16% of the margins of one or a few gills arches (Figure the individuals aged 0+ and 1+). The mean 7). These deformations were accompanied by number of gill rakers on the first gill arch in the presence of thin and plicate margin of the this group of hybrids aged 0+ was 18.40 (13- branchiostegal membrane. The deformations 23) and in those aged 1+ it was 18.82 (11-23). and losses were most often seen in one and rarer in two opercular bones. Distinct Pyloric caeca deformations were also identified in the Analysis of the pyloric caeca has revealed partition of the branchiostegal membrane deformations in their structure in the majority which was much overgrown and swollen of individuals. The deformed pyloric caeca downwards causing distortions to the oral were of different length, from very short and cavity and the profile of the fish (Figure tumorous (slightly bulging the wall of the 8). In many hybrids these changes were alimentary track) (Figure 3) to long thread- accompanied with the loss in the lamellae arch like and were unevenly distributed (Figure branch or their underdevelopment. Often, the 4). The deformations were observed in 92.5% deformations in the gill sac occurred together of trout x salmon hybrids aged 0+ and 99% with those in the branchiostegal membrane of those aged 1+ (94% of all trout x salmon leading to a shortening of the interopercular hybrids). The mean number of pyloric caeca bone. in trout x salmon hybrids aged 0+ was 24.97 (5-55), while in those aged 1+ it was 21.02 Among the trout x salmon hybrids the internal (9-54). Similar anomalies in pyloric caeca deformations were noted in 23% of individuals were observed in salmon x trout hybrids; in aged 0+ and 36.6% of those aged 1+, whereas 57% of those aged 0+ and 60% of those aged among the salmon x trout ones the internal 1+ (in total 58% of all hybrids of this type). deformations were detected in 26% of those In the hybrids aged 0+ the average number of aged 0+ and 16% of those aged 1+. Statistical pyloric caeca was 33.66 (14-45). Similarly as analysis of the Pearson linear correlations in the trout x salmon hybrids, in individuals STATISTICA (data analysis software system), aged 1+ this number was 29.03 (11-41) and version 8.0. www.statsoft.com., StatSoft, lower than for those aged 0+. Inc. (2007) between the body length and the number of gill rakers, mass of the fish and the Internal deformations number of gill rakers, the body length and In the hybrids of both types also internal the number of pyloric caeca and the body deformations in the branchiostegal membrane mass and the number of pyloric caeca in and the opercular bones were also observed. particular hybrids aged 0+ and 1+ proved no The membrane suffered some shortening correlations, the correlation coefficient > 0.2). and in some individuals it was folded up or The exception is a correlation between the down. In the operculum there was loss in mass of salmon x trout hybrids aged 1+ and individual bones: opercular, interopercular the number of pyloric caeca, characterised by or subopercular (Figure 5), or in all opercular the correlation coefficient r=0.6. Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 158

a

120 100 80 60

% hybrids 40 20 0 0+ 1+ 0+ i 1+ age pyloric caeca external first arch branch total

b

90 80 70 60 50 40

% hybrids 30 20 10 0 0+ 1+ 0+ i 1+ age pyloric caeca external first arch branch total

Fig. 9. Deformations in the ♀ Salmo trutta m. trutta x ♂ Salmo salar hybrids (a) and ♀ Salmo salar x ♂ Salmo truttam. trutta hybrids (b) in the first and second year of life. Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 159

To sum up, the deformations observed in deformations including those in the head and reciprocal hybrids of salmon and trout consequently higher mortality were found concerned most often the pyloric caeca (94 in the trout x salmon hybrid than in the % of trout x salmon hybrids and 58 % of reciprocal one. The anomalies of the first arch salmon x trout hybrids). The anomalies in branch in the form of the lack of gill rakers and the first arch branch were noted in 52% of their irregular distribution were reported by trout x salmon hybrids and 12% of salmon x Kazakov et al.(1984) in the reciprocal salmon trout ones, whereas the internal deformations x trout hybrids but of unknown direction of in 27% and 22 %, respectively. The percent hybridisation. Changes in the first gill arch are of trout x salmon hybrids with at least one related to a lower number of the gill rakers type deformation increased with age and on the first arch. The hybrids we studied had reached 94% of individuals aged 0+ and 99% the number of gill rakers lower than trout individuals aged 1+ (95.3% of all trout x salmon aged 0+ and 1+ having 15- 20 ones (Kirczuk hybrids). Among the salmon x trout hybrids & Domagała 2003) and than salmon having the deformations were observed in 66% of 16-22 ones (Domagała & Kirczuk 2004). The individuals aged 0+ and 77% of individuals deformations of the oral cavity observed in aged 1+ (altogether in 70% of salmon x trout the reciprocal hybrids of salmon and trout hybrids), Tab. 2. were observed in 17% of the hybrids of Hypophthalmichtys nobilis x Ctenopharyngodon Discussion idella, which also had deformed fins, twisted Characteristic features of many fish hybrids head and bent body preventing further are the anomalies appearing at different stages development (Bakos et al. 1978). Numerous of development. The disturbances leading to hybrids of rhodurus x total mortality prior to the stage of hatching fontinalis (Iuchi et al. 1975) were found to have been reported to occur, e.g. in the hybrids have deformations in the head and spine, of Oncorhynchus kisutch x Salmo gairdneri, while the hybrids of Ctenopharyngodon idella Oncorhynchus kisutch x Salmo trutta, Salmo x Hypophthalmichthys nobilis had mainly truttax Salmo gairdneri (Blanc, Chevassus 1979; deformations of the spine and jaw, rarely of Chevassus 1979). Also Gray et al. (1993) on the the opercular bones and the gills (Beck et al. basis of analysis of a few dozens hybrids of 1984). According to Bakos et al.(1979) and the salmonids have reported high proportions Hardy (1999), the shortening of the gill cover of hybrids with deformations, in particular in and deformations of the jaw joints in the the groups of a low percent of survivability. salmon causing impairment in the function of Our analysis of the salmon and trout hybrids oral cavity, which implies problems with food has shown that nearly 100% of trout x salmon intake and increased mortality. The hybrids and 70% of salmon x trout hybrids revealed of Ictalurus punctatus x I. furcatus revealed deformation of at least one type: pyloric caeca, deformations in the caudal fin, but they first gill arch or external head deformations. were considered to be related to the less than As follows from the study by McGowan & optimal conditions in the fish farming as the Davidson (1992) and Gray et al. (1993) more same anomalies were noted also in the parent Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 160

Beall E, Moran P, Pendas A, Izquierdo J and species of I. punctatus (Goudie et al. 1993). Also Garcia-Vazquez E (1997). L’hybridation dans Sutterlin et al. (1987) related the deformations les populations naturelles de Salmonidés in the opercular bones and jaw of the hybrids dans le sud-ouest de L’Europe ET en milieu of not migrating to the sea and anadromic experimental. Bulletin Francais De La Peche Et De La Pisciculture 344/345, 271-285. salmon with the conditions of growth (poorer condition, stress, reduced content of oxygen Beck ML, Biggers CJ and Barker CJ (1984). and limited motion) and to some degree with Chromosomal and electroforetic analyses of the triploidal character of the hybrids. This hybrids between grasskarp and bighead carp (Pisces: Cyprinidae). Copeia 2, 337-342. interpretation is supported by the results obtained for salmon cultured in the farms Blanc JM (2003). Paternal variation in juvenile revealing deformations of the opercular bones survival and growth the triploid hybrid and jaw being a consequence of improper between female (Oncorhynchus mykiss Walbaum) and male (Salmo diet (Hardy 1999). The reciprocal hybrids trutta L.). Aquaculture Research 34, 205-210. of salmon and trout studied were found to have deformed pyloric caeca occurring in a Blanc JM and Chevassus B (1979). Interspecific lower number than trout (29-69 pyloric caeca) hybridization of Salmonid fish. I. Hatching and survival up to the 15th day after hatching (Kirczuk & Domagała 2003) and salmon (51- in F1 generation hybrids. Aquaculture 18, 21- 77) (Domagała & Kirczuk 2004). None of the 34 deformations observed in these hybrids had been reported earlier in any of the pure species Chevassus B (1979). Hybridization in salmonids: results and perspectives. (Kirczuk & Domagała 2003), (Domagała & Aquaculture 17, 113-128. Kirczuk 2004) incubated and growing in the same conditions, in watercourses in the Delling B, Crivelli AJ, Rubin JF and Berrebi Pomerania district. Results of the studies P (2000). Morphological variation in hybrids between Salmo marmoratus and alien Salmo performed on so numerous group of hybrids species in the Volarja stream, Soca River basin, collected from many experiments have . Journal of Fish Biology 57, 1199-1212. shown that the deformations observed are the consequence of crossing, which confirms Domagała J and Kirczuk L (2004). Morphological characterisation of salmon that this process is undesirable and should be (Salmo salar L., 1758) aged 0+, 1+ and 2+, prevented. The analysis indicates that hybrids stocked in Pomeranian rivers. Electronic should be treated as a threat to pure species Journal of Polish Agricultural Universities Series and points to the necessity of developing and Fisheries 7, 1 (www.ejpau.media.pl). applying measures to prevent this undesirable Elo K, Erkinaro J, Vuorinen J and Niemela phenomenon. E (1995). Hybridization between Atlantic salmon (Salmo salar) and brown trout (S. References trutta) in the Teno and Näätämö River Bakos J, Krasznai Z and Márián T (1978). Cross Systems, northernmost Europe. Nordic Journal –breeding experiments with carp, tench and of Freshwater Research 70, 56-61. Asian phytophagous cyprinids. Aquaculture Hungarica (Szarvas) 1, 51-57. Galbreath PF and Thorgaard GH (1994). Viability and freshwater performance of Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 161

Atlantic salmon x Brown trout triploid Andersson T (1991). High frequency of hybrids. Canadian Journal of Fisheries and natural hybrids between Atlantic salmon Aquatic Sciences 51(1), 16-24. Salmo salar L., and brown trout, Salmo trutta L., in a Swedish river. Journal of Fish Biology 39 Garcia de Léaniz C and Verspoor E (1989). (Suppl A), 343- 348. Natural hybridization between Atlantic salmon, Salmo salar, and brown trout, Salmo Jansson H and Öst T (1997). Hybridization trutta, in northern Spain. Journal of Fish Biology between Atlantic salmon (Salmo salar) and 34, 41-46. brown trout (Salmo trutta) in a restored section of the River Dalälven, Sweden. Canadian Garcia-Vazquez E, Ayllon F, Martinez J, Journal of Fisheries and Aquatic Sciences 54, Perez J and Beall E (2003). Reproduction 2033-2039. of interspecific hybrids of Atlantic salmon and brown trout in a stream enviroment. Kazakov RV, Ilyenkowa SA and Kozlow VV Freshwater Biology 48, 1100-1104. (1984). Osobiennosti morfologiï rzabiernykh ticzinok u gibridov atlantichieskogo Garcia-Vazquez E, Moran P, Perez J, Martinez lososya Salmo salar c kumzhiey Salmo trutta JL, Izquierdo JL, Gaudemar B and Beall (Salmoniformes, ). Zoologitchieskiï E (2002). Interspecific barriers between zhurnal LXIII(2), 306-309 (In Russian). salmonids when hybridization is due to sneak mating. Heredity 89, 288-292. Kirczuk L and Domagała J (2003). Characteristics of young (Salmo trutta Goudie CA, Tiersch, TR and Simco BA m. trutta L. 1758) growing in Pomeranian (1993). Early growth and morphology among rivers to the smolt stage. Electronic Journal of hybrids of Ictalurid catfishes.Journal of Applied Polish Agricultural Universities Series Fisheries Aquaculture 3, 235-255. 6, 1.

Gray AK, Evans MA and Thorgaard GH Makhrov AA, Kuzishchin KV and Novikov (1993). Viability and development of diploid GG (1998). Natural hybrids of Salmo salar and triploid salmonid hybrids. Aquaculture with Salmo truttain the rivers of the White Sea 112, 125-142. Basin. Journal of Ichthyology 38(1), 61-66.

Hammar J, Dempson JB and Verspoor E (1991). McGowan C and Davidson WS (1992). Artificial Natural hybridization between hybridization of Newfoundland brown trout (Salvelinus alpinus) and (Salvelinus and Atlantic salmon: hatchability, survival fontinalis): evidence from Northern Labrador. and growth to first feeding. Aquaculture 106, Canadian Journal of Fisheries and Aquatic Sciences 117-125. 48, 1437-1445. Semenova SK and Slyn’ko VI (1988). Protein Hardy RW (1999). Fish, feed and nutrition- Polymorphism in Salmo salar L. and Salmo problems and opportunities in fish feed trutta L. Populations and their Hybrids. formulation. Aquaculture Magazine 7/8, 56- 60. Genetika 24(3), 548-555.

Iuchi I, Suzuki R and Yamagami K (1975). Sutterlin AM, Mac Farlane LR and Harmon Ontogenic expression of larval and adult P (1977). Growth and salinity tolerance in hemoglobin phenotypes in the intergeneric hybrids within Salmo sp. and Salvelinus sp. salmonid hybrids. Journal of Experimental Aquaculture 12, 41-52. Zoology 192(1), 57-64. Verspoor E (1988). Widespread hybridization Jansson H, Holmgren I, Wedin K and between native Atlantic salmon, Salmo salar, Bull. Eur. Ass. Fish Pathol., 29(5) 2009, 162 and introduced brown trout, S. trutta, in eastern Newfoundland. Journal of Fish Biology 32, 327-334.