Observations of Eurasian perch (Perca fluviatilis L.) post-larvae growth performances reared in an illuminated floating cage in Varese lake (N-W Italy) over a two years period

Figures & data

Figure 1 Bathymetric map, principal hydrologic characteristics of Varese lake and cage position during the trials.

Table 1 Chemical and physical water parameters monitored during the samplings in 2006 and 2007.

Depth	Temperature (°C)		O2(mg L^−1)		% Sat.		pH
	2006	2007	2006	2007	2006	2007	2006	2007
Surface	22.48±0.58	23.35±1.75	8.89±1.08	9.51±2.04	105.96±19.52	113.00±25.53	9.21±0.25	9.22±0.26
1 m	22.35±0.83	23.48±1.94	8.78±1.74	9.46±1.99	102.88±18.35	112.96±24.97	9.19±0.18	9.22±0.24
2 m	22.38±1.15	23.46±2.05	8.75±1.31	8.80±1.80	100.58±18.36	105.96±21.39	9.24±0.20	9.26±0.24
3 m	22.48±1.38	23.32±2.11	7.62±1.41	7.56±1.38	86.88±21.58	86.20±24.93	9.21±0.22	9.21±0.20
4 m	22.30±1.22	22.54±1.78	5.10±1.98	5.29±2.20	59.95±21.02	61.22±27.37	8.88±0.22	8.91±0.21
5 m	22.15±1.78	22.53±1.70	3.58±2.12	3.87±2.43	44.01±22.24	44.92±28.72	8.43±0.17	8.85±0.19
7 m	19.20±0.98	19.68±1.15	0.18±1.58	0.26±0.49	2.60±6.01	3.00±6.02	8.40±0.15	8.61±0.20

Table 2 Data on perch post-larvae reared in the illuminated cage 2006 and 2007.

Variables	2006	2007
No. of larvae	280	300
Initial post-larvae length, cm	4.30±0.33	2.80±0.31^*
Initial post-larvae weight, g	0.64±0.09	0.25±0.082^*
Final fry length, cm	7.47±0.96	8.1±0.73^*
Final fry weight, g	4.65±1.47	6±1.88^*
SGR, %	2.04	3.42
Survival, %	50.7	60.7

* (P<0.05) between 2006 and 2007 data.

Figure 2 Trend of perch fry weight on 2006 (grey) and 2007 (black) during the rearing period in the illuminated floating cage (*P<0.05).

Figure 3 Weight comparison between wild and reared perch (2006–2007) at the end of the trials (different letters indicates significant differences P<0.05).

Table 3 Zooplankton densities assessed inside the cage and in the control point during the 24 h sampling (2006 and 2007). Different letters indicates significant differences (P<0.05) in number of zooplankters between the sampling points during the night time.

	Number of zooplankters L^-1
Day time	Inside the cage		Control point (15 m from the cage)
	2006	2007	2006	2007
8.00	7±2	7±1	11±5	8±1
10.00	5±3	6±3	15±2	5±3
12.00	4±2	4±2	14±5	5±3
14.00	4±3	12±0	22±4	22±1
16.00	12±2	9±5	22±5	10±4
18.00	3±2	10±1	13±5	9±2
20.00	8±4	6±1	28±3	7±3
22.00^*	45±6^a	33±5^a	26±7^a	28±3^a
23.00	135±10^a	145±13^a	16±11^b	33±4^b
1.00	525±26^a	521±11^a	41±22^b	50±7^b
3.00	406±21^a	400±31^a	65±9^b	60±6^b
5.00	82±9^a	65±8^a	30±14^b	48±13^b
7.00	5±3^a	2±4^a	17±9^b	13±5^b

* Light switch on.

Figure 4 Zooplankton density in the cage and in a control point, during the night in 2006 (a) and in 2007 (b). Different letters indicate significant differences (P<0.05) in number of zooplankters between the sampling points. The symbol (*) indicates significant differences in zooplankton accumulation inside the cage between the two years at the same day time.

Table 4 Comparison of perch females and males total length between Como lake (Negri, 1999) and Varese lake (Ceccuzzi, 2007).

Como lake
Males	Females
Age (years)	T. length (cm)	Age (years)	T. length (cm)
1	9	1	9
2	14	2	14.5
3	15.6	3	17.4
4	17.5	4	19.4

Varese lake
Males	Females
Age (years)	T. length (cm)	Age (years)	T. length (cm)
1	15	1	15.8
2	17.3	2	18.5
3	18.9	3	20.9
4	22.1	4	23.8

NegriA 1999 Biologia ed Ecologia del persico reale (P. fluviatilis) nel Lago di Como Home page address: http://www.provincia.como.it.

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CeccuzziP. 2007 Biology and Ecology of Eurasian perch (Perca fluviatilis) in Varese Lake PhD Thesis Università dell'Insubria Varese, Italy

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